Digital thermal binder and powder printing

ABSTRACT

A method of forming a digital print on a surface ( 2 ) by applying powder of dry ink ( 15 ) including colourants ( 7 ) on the surface, bonding a part of the dry ink ( 15 ) powder to the surface ( 2 ) by a digital heating print head ( 80 ) such that the digital print is formed by the bonded dry ink colourants ( 7 ) and removing non-bonded dry ink ( 15 ) from the surface ( 2 ).

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.14/152,356, filed on Jan. 10, 2014, which claims the benefit of U.S.Provisional Application No. 61/751,418, filed on Jan. 11, 2013. Theentire contents of U.S. application Ser. No. 14/152,356 and U.S.Provisional Application No. 61/751,418 are hereby incorporated herein byreference in their entirety.

TECHNICAL FIELD

The disclosure generally relates to the field of digitally createddecorative surfaces for building panels such as floor and wall panels.The disclosure relates to a method to apply and bond powder basedcolourants on a surface such that a digital print is formed.

FIELD OF APPLICATION

Embodiments of the present invention are particularly suitable for usein floors, which are formed of floor panels comprising a core or a body,a decorative layer and preferably a transparent wear resistantstructured layer above the decorative layer. Preferred embodiments areconventional laminate floors, powder based floor, wood floors, plasticbased LVT floors and ceramic tiles. The following description oftechniques, problems of known technology and objects and features of theinvention will therefore, as a non-restrictive example, be aimed aboveall at this field of application and in particular at floorings whichare similar to conventional laminated floorings or floorings with aresilient surface layer.

It should be emphasized that embodiments of the invention may be used toproduce a digital image and/or a digitally formed structure on anysurface but flat panels such as, for example, building panels ingeneral, wall panels, ceilings, furniture components and similarproducts that generally have large surfaces with advanced decorativepatterns are preferred. The basic principles of the invention may beused to apply a print on paper, foils, textiles, metals, solid wood,wood veneer, wood based sheet materials, cork, linoleum, polymermaterial, ceramics, wall paper and similar surfaces.

BACKGROUND

The following description is used to describe the background andproducts, materials and production methods that may comprise specificparts of preferred embodiments in the disclosure of this invention.

a) Laminate Floorings.

The majority of all laminate floors are produced according to aproduction method generally referred to as Direct Pressed Laminate(DPL). Such laminated floors have a core of 6-12 mm fibreboard, a 0.2 mmthick upper decorative surface layer of laminate and a 0.1-0.2 mm thicklower balancing layer of laminate, plastic, paper or like materials.

The surface layer of a laminate floor is characterized in that thedecorative and wear properties are generally obtained with two separatelayers of paper, one above the other. The decorative layer is generallya printed paper and the wear layer is a transparent overlay paper, whichcomprises small aluminium oxide particles.

The decor paper is the most critical of the lamination papers as itgives the visual appearance of the laminate. The decor paper weight isgenerally in the range of 60-150 g/m².

The overlay paper is generally thinner with a weight of about 20-50 g/m²and is made of pure cellulose, which is based on delignified pulp. Theoverlay paper becomes almost completely transparent after lamination andthe appearance of the decor paper is visible. Thicker overlay paperswith a considerable amount of aluminium oxide particles may give a highwear resistance. The disadvantage is that they are less transparent andthe decorative pattern is covered by a grey layer that disturbs theprinted pattern.

Printing of decorative papers is very cost efficient. Rotogravurepresses with printing cylinders that may have a width of 3 metres andthat may run with a speed of up to 600 m/min are used. The printingcylinders are generally produced by conventional mechanical engraving.Recently digital laser engraving has been introduced which allows fasterdécor development and provides a better décor quality. Solvent-free inkswith organic pigments are often used and excess ink is re-cycled.

The printed decorative paper and the overlay are impregnated withmelamine formaldehyde resins, generally referred to as melamine resins,and laminated to a HDF core in large discontinuous or continuouslaminate presses where the resin cures under high heat (about 170° C.)and pressure (40-60 bars) and the papers are laminated to the corematerial. An embossed press plate or steal belt forms the surfacestructure. Sometimes a structured paper is used as a press matrix. Theembossing is in high quality floors made in register with the design.The embossing depth is limited to 0.1-0.2 mm (100-200 micron).

Laminated floors may also be produced with direct printing technology.One advantage is that the pressing operation may be avoided and that noprinted papers are needed to provide a decorative surface. Hydroprinting inks are used to print the décor by a multicolour printingpress with rollers onto a pre-sealed core and the print is covered witha protective transparent wear layer that may be an overlay, a plasticfoil or a lacquer. The production process is rather complicated and isonly cost efficient in very large production volumes.

Direct printing technology may be replaced with digital printingtechnology that is much more flexible and small production volumes canbe economically manufactured. The difference between these two methodsis mainly the printing step where the printing rollers are replaced by adigital non-contact printing process.

Digital printing may also be used to print on a paper sheet that is usedin conventional laminate production and laminated under heat andpressure. The printing may be made prior or after impregnation. Suchprinting prior to impregnation is complicated since paper may swell andshrink during the printing and impregnation step and small quantitiesare not cost efficient to impregnate. Printing after impregnation on amelamine impregnated paper is very difficult since pigments applied on amelamine surface float during the pressing step when the melamine resinis in a liquid state. Such problems may partly be solved with a methodwhere a raw paper, preferably comprising a base colour, is applied andfixed to the core prior to printing and impregnated paper or melaminepowder is applied under and/or over the raw paper such that the resinsfrom the impregnated papers penetrate into the raw paper during thepressing step.

Laminate floors may also have a surface of paper foils or plastic foilsand such foil materials may also be printed digitally. A protective wearresistant transparent layer that generally is a polyurethane lacquer isused to covers the printed décor.

b) Powder Based Floors (WFF)

Recently new “paper free” floor types have been developed with solidsurfaces comprising a substantially homogenous powder mix of fibres,binders and wear resistant particles hereafter referred to as WFF (WoodFibre Floor).

The powder mix may comprise aluminium oxide particles, melamineformaldehyde resins and wood fibres. In most applications decorativeparticles such as, for example, colour pigments are included in the mix.In general, all these materials are applied in dry form as a mixedpowder on a HDF core and cured under heat and pressure to a 0.1-1.0 mmsolid layer. The powder is, prior to pressing, stabilized with moistureand IR lamps such that it forms an upper skin layer similar to a paperlayer and this prevents the powder from blowing away during pressing.Melamine formaldehyde powder and wood fibres may be replaced bythermoplastic particles.

Several advantages over known technology and especially overconventional laminate floorings may be obtained such as increased wearand impact resistance, deep embossing, increased production flexibilityand lower costs. An embossing depth of 0.2-0.7 mm may easily be reached.

Powder technology is very suitable to produce a decorative surfacelayer, which is a copy of stone and ceramics. In the past it was moredifficult to create designs such as, for example, wood decors. However,recently digital powder printing has been developed and it is possibleto create very advanced designs of any type by injecting ink into thepowder prior to pressing. Problems related to paper impregnation may becompletely eliminated since no impregnation is required. The surfacestructure is made in the same way as for laminate flooring by astructured press plate, a steal belt or an embossed matrix paper that ispressed against the powder. A major advantage compared to the otherdigital printing technologies is that the powder provides a base colourand no protective layer is needed above the print since the ink maypenetrate into the powder. The penetration is however rather limitedsince the ink drops will be bonded to the first particle that they hit,mainly the wood fibres. Increased wear resistance may be reached ifseveral printed powder layers are applied on each other or if a powderoverlay is used as a protective layer applied over the digital print.

c) Melamine Formaldehyde Resin.

A basic substance in Laminate and WFF floors is the thermosettingmelamine formaldehyde resin that is used as a binder. Melamine resin ormelamine formaldehyde resin (generally shortened to melamine) is a hard,thermosetting plastic material made from melamine and formaldehyde bypolymerization. Such resin, hereafter referred to as melamine, comprisesthree basic stages. The stages, A-stage, B-stage, C-stage are describedin Principles of Polymerization, George Odian, 3rd edition, which ishereby incorporated by reference, including particularly pages 122 to123. The first uncured A-stage is obtained when melamine, formaldehydeand water is boiled to a liquid substance with a dry content of about50%. The second semi-cured B-stage is obtained when the liquid resin isused to impregnate, for example, an overlay paper that after theapplication of the liquid resin is dried with heat. The molecules havestarted to cross link but the resin is still possible to cure in a finalstage if the drying of the resin is made during a rather short time, forexample, one minute and with a heat of about 90-120° C.

The B-stage may also be obtained by spraying the liquid resin over hotair such that the drops are dried and a dry semi-cured melamineformaldehyde powder is obtained that comprises small round sphericalparticles with a diameter of about 30-100 microns (0.03-0.10 mm).

The final completely cured C-stage is obtained when, for example, themelamine impregnated paper or the WFF powder is heated to about 160° C.under pressure during 10-20 seconds. The dry melamine formaldehyde resinbecomes softer, melts and cures to a fixed form when the temperatureincreases during the pressing. The curing is dependent on temperatureand heating time. Curing may be obtained at lower temperatures andlonger time or at higher temperature during shorter time. Spray driedmelamine powder may also be cured under high temperature.

d) Wood Floors.

Wood floors are produced in many different ways. Traditional solid woodfloors have developed into engineered floors with wood layers applied ona core made of wood lamellas, HDF or plywood. The majority of suchfloors are delivered as pre-finished floors with a wood surface that iscoated with several transparent layers in the factory. The coating maybe made with UV cured polyurethane, oil or wax. Recently wood flooringshave also been produced with a digitally printed pattern that improvesthe design of the wood grain structure in wood species that do not havea sufficient surface quality.

e) Ceramic Tiles

Ceramic tiles are one of the major materials used for flooring and wallcoverings. The raw materials used to form tiles consist of clayminerals, feldspar and chemical additives required for the shapingprocess. One common method to produce ceramic tiles uses the followingproduction steps. The raw materials are milled into powder and mixed.Sometimes, water is then added and the ingredients are wet milled. Thewater is removed using filter pressing followed by spray drying intopowder form. The resulting powder is then dry pressed under a very highpressure (about 400 bars) to a tile body with a thickness of 6-8 mm. Thetile body is further dried to remove remaining moisture and to stabilizethe tile body to a solid homogenous material. Recently dry pressing oflarge and thin panels have been introduced. Dry granular material ispressed with very high pressure up to 400 bars and panels with a size of1*2 m and more and with thicknesses down to a few mm may be produced ina cost efficient way. Such panels may be used for wall panels andworktops. The production time has been reduced from several days to lessthan an hour. Such panels may be cut and shaped with productiontolerances that are superior to the traditional methods and the may evenbe installed in a floating manner with mechanical locking systems. Oneor several layers of glaze, which is a glass like substance, are appliedon the tile body by dry or wet methods. The thickness of the glazing isabout 0.2-0.5 mm. There may be two glazes on the tile, first anon-transparent glaze on the tile body, then a transparent glaze on thesurface. The purpose of tile glazing is to protect the tile. The glazeis available in many different colours and designs. Some glazes cancreate different textures. The tile is after glazing fired in a furnaceor kiln at very high temperatures (1,300° C.). During firing, the glazeparticles cures and melt into each other and form a wear resistantlayer. Roller screens are often used to create a decorative pattern. Thecontact nature of the rotary screen-printing has many disadvantages suchas breakages and long set-up times. Several tile producers havetherefore recently replaced this conventional printing technology withdigital ink jet printing technology that offers several advantages.Generally oil based inks are used and the print is applied on thepressed tile body or on a base glazing that is applied in wet form anddried prior to printing. A transparent glaze layer may be applied on thedigital print in order to improve the wear resistance. Digitalnon-contact printing means no breakages and possibility to use thinnertile bodies. Short set-up times, randomized printing with no repetitioneffects and ability to print on surfaces of variable structures and ontiles with beveled edges are other major advantages.

Additional circumstances that have contributed to the introduction ofthe digital printing technology in the tile industry is the fact thatceramic tiles are rather small compared to, for example, laminate andpowder based floors that are produced as large pressed boards of about2.1*2.7 m. Rather small printers with limited number of print heads maybe used in the tile industry and the initial investment is ratherlimited. Oil based inks have a very long drying time and clogging ofnozzles may be avoided. Other advantages are related to the glazing thatprovides a base colour. Generally smaller amounts of pigments arerequired to form a tile pattern on a base colour than to provide anadvanced wood grain design on a HDF or paper material used in laminatefloorings where impregnation and lamination creates additional problems.

f) LVT Floorings.

Luxury Vinyl Tiles, generally referred to as LVT floorings, areconstructed as a layered product. The name is somewhat misleading sincea major part of LVT floors have a plank size with a wood pattern. Thebase layer is made primarily of several individual base layerscomprising different mixtures of PVC powder and chalk filler in order toreduce material costs. The individual base layers are generally about 1mm thick. The base layer has a thin high quality printed decorative PVCfoil on the upper side. A transparent wear layer of vinyl with athickness of 0.1-0.6 mm is generally applied on the decorative foil.Glass fibres are often used to improve thermal stability. The individualbase layers, glass fibres, the decorative foil and the transparent layerare fused together with heat and pressure in continuous or discontinuouspresses. The transparent layer may include a coating of polyurethane,which provides additional wear and stain resistance. Some producers havereplaced the transparent vinyl layer with a polyurethane layer that isapplied directly on the decorative foil. Recently new types of LVTfloors have been developed with a base layer thickness of 3-6 mm andwith edges comprising mechanical locking systems that allow floatinginstallations. LVT floors offer several advantages over, for example,laminate floors such as deep embossing, flexibility, dimensionalstability, moisture resistance and lower sound. Digital printing of LVTfloors is only on an experimental stage but would, if introduced,provide major advantages over conventional printing technology.

As a summary it may be mentioned that digital printing is used inseveral floor types to create a décor. However the volumes are stillvery small, especially in wood and laminate flooring applications,mainly due to high cost of the ink and high investment cost for theindustrial printers. The flexibility that the digital printingtechnology provides is limited by the embossing that is fixed and notpossible to adapt to the variations of the digitally printed décor. Itwould be a major advantage if the ink cost could be reduced, if morecost efficient printing equipment could be used in an industrial scale,if a higher wear resistance could be reached without separate protectivelayers and if variations in the embossed structures may be formed thatcorrespond to variations in the digitally printed pattern.

DEFINITION OF SOME TERMS

In the following text, the visible surface of the installed floor panelis called “front side”, while the opposite side of the floor panel,facing the sub floor, is called “rear side”.

By “up” is meant towards the front side and by “down” towards the rearside. By “vertically” is meant perpendicular to the surface and by“horizontally” parallel to the surface.

By “pigments” is meant a very fine powder of solid colorant particles.

By “pigment ink” is meant an ink comprising pigments that are suspendedor dispersed throughout a carrier fluid.

By “binder” is meant a substance that connects or contributes to connecttwo particles or materials. A binder may be liquid, powder based, athermosetting or thermoplastic resin and similar. A binder may consistof two components that react when in contact with each other. One of thecomponents may be liquid and the other dry.

By “matrix” also called “mat” is meant a material that forms an embossedsurface structure when the material is pressed against a surface.

By “Embossed In Register” or EIR means that a printed décor is inregister with an embossed structure.

By “digital ink jet printing” is meant a digitally controlled ejectionof drops of fluid comprising a colorant from a print head onto asurface.

By “digital print” is meant a digitally controlled method to positioncolorant onto a surface.

By “colourant” is meant any material (dye, organic or inorganicpigments, small coloured particles of any material etc.) that may beused to provide a colour on a surface preferably due to selectiveabsorption or reflection of different wavelengths of light.

By “panel” is meant a sheet shaped material with a length and width thatis larger than the thickness. This rather broad definition covers, forexample, laminate and wood floors, tiles, LVT, sheet shaped wallcoverings and furniture components.

Known Technique and Problems Thereof

The generally known technologies, which may be used to provide a digitalprint and an embossed surface structure, are described below. Themethods may be used partly or completely in various combinations withpreferred embodiments of the invention in order to create a digitalprint or a digital embossing according to this disclosure of theinvention.

High definition digital ink jet printers use a non-impact digitalprinting process. The printer has print heads that “fire” drops of inkfrom the print head to the surface in a very precise manner.

Multipass Printing, also called scanning printing, is a printing methodwhere the printer head moves transverse above the surface many times togenerate an image. Such printers are slow but one small print head cangenerate a bigger image.

Industrial printers are generally based on a Single Pass Printingmethod, which uses fixed printer heads, with a width that corresponds tothe width of the printed media. The printed surface moves under theheads. Such printers have a high capacity and they are equipped withfixed print heads that are aligned one after each other in the feedingdirection. In general each head prints one colour. Such printers may becustom made for each application.

FIG. 1a , shows a side view of an industrial single pass digital ink jetprinter 35 comprising five digital print heads 30 a-e, which areconnected with ink pipes 32 to ink containers 31 that are filled withink of different colours. The ink heads are connected with digital datacables 33 to a digital control unit 34 that controls the application ofthe ink drops and the speed of the conveyor 21 that must be able todisplace the panel under the print heads with high precision in order toguarantee a high quality image comprising several colours.

FIG. 1b shows a top view of a wood grain print P provided on a panelsurface 2. The surface of a floor panel is often embossed with a basicstructure 17 that is the same for several basic decors as shown in FIG.1c . Advanced floors use a so-called EIR (Embossed In Register)embossing 17 that is coordinated with the printed pattern P as shown inFIG. 1 d.

A normal width of an industrial print head is about 6 cm and any lengthsmay be printed. Wide areas of 1-2 m may be printed with digital printerscomprising several rows of print heads aligned side by side. 166 printheads may be needed to provide a 5-colour print on a 2 m wide laminatefloor panel and the print may be destroyed if only a few nozzles in oneprint head are blocked by dry ink.

Number of dots per inch or DPI is used to define the resolution and theprinting quality of a digital printer. 300 DPI is generally sufficientto, for example, print wood grains structures of the same qualitypresently used in conventional laminate floorings. Industrial printerscan print patterns with a resolution of 300-600 DPI and even more andwith a speed exceeding 60 m/min.

The print may be a “full print.” This means that the visual printeddécor is mainly created by the ink pixels applied on the surface. Thecolour of a powder layer or a base colour of a paper has in such anembodiment, in general, a limited effect on the visible pattern ordécor.

The print may also be a “part print”. The colour of another underlyinglayer is one of the colours that are visible in the final décor. Thearea covered by printed pixels and the amount of ink that is used may bereduced and cost savings may be obtained due to lower use of ink andincreased printing capacity compared to a full print design. However apart print is not as flexible as a full print since the base colours aremore difficult to change than when a full print is used.

The print may be based on the CMYK colour principle where the whitecolour is provided by the surface. This is a 4-color setup comprisingcyan, magenta, yellow and black. Mixing these together will give acolour space/gamut, which is relatively small. To increase specificcolour or the total gamut spot colours may be added. A spot colour maybe any colour. The colours are mixed and controlled by a combination ofsoftware and hardware (print engine/print heads). The flexibility mayalso be increased considerably by adding a white colour to the printer.

New technology has been developed by CeraLoc Innovation Belgium BVBA, asubsidiary of Valinge International AB that makes it possible to injecta digital liquid print into a powder layer. This new type of “DigitalInjection Print” or DIP is obtained due to the fact that printing ismade into a powder that is cured after printing. The ink and the printare embedded into the cured layer and they are not applied on a layer aswhen conventional printing methods are used. The print may be positionedin several dimensions horizontally and vertically in different depths.This may be used to create 3D effects when, for example, transparent andpreferably bleached wood fibres are used. A two-layer print may also beused to increase the wear resistance. No protective layers of, forexample, overlay are needed that disturb the original design with greyshadings.

The DIP method may be used in all powder based materials, which may becured after printing. However, the DIP method is especially suitable tobe used when the powder comprises a mix of wood fibres, small hard wearresistant particles and a melamine resin. The surface layer may alsocomprise thermoplastic material, for example, vinyl particles, which areapplied in powder form on a surface. This allows that the print may beinjected in the vinyl powder particles. An improved design and increasedwear resistance may be reached even in such materials.

A suitable printer head has to be used in order to obtain a highprinting quality and speed in powder based layers and other layers asdescribed above. A printer head has several small nozzles that can shootand apply droplets of inks in a controlled way.

Industrial inkjet systems, are broadly classified as either continuousinkjet (CIJ) or drop on demand (DOD) systems.

CIJ ejects drops continuously from the print head. The drops passthrough a set of electrodes, which impart a charge onto each drop. Thecharged drops then pass a deflection plate which uses an electrostaticfield to select drops that are to be printed and drops to be collectedand returned for re-use.

DOD ejects drops from the print head only when required and all dropsare applied on the surface.

CIJ is primarily used for coding and marking of products. DOD inkjettechnology is currently used in most existing industrial inkjetapplications where a high quality décor is required.

A normal size of an ink droplet is about 2-4 picolitres (=1*10⁻¹² litreor 0.000001 mm³). The size of each droplet may vary, dependent on inktype and head type, normally between 1-40 picolitres and thiscorresponds to a droplet that has a diameter of about 10-30 microns.Smaller droplets enable high-resolution images. Some printer heads canshoot different droplet sizes and they are able to print a grey scale.Other heads can only shoot one fixed droplet size. It is possible todesign print heads that may fire bigger drops up to 100-200 picolitresor more.

Several technologies may be used to shoot the drops out of the nozzles.

Thermal print head technology generally referred to as bubble jetprinting, use print cartridges with a series of tiny chambers eachcontaining a heater. To eject a droplet from each chamber, a pulse ofcurrent is passed through the heating element causing a rapidvaporization of the ink in the chamber to form a bubble, which causes alarge pressure increase, propelling a droplet of ink out through thenozzle and to the surface. Most consumer inkjet printers use thermalprinter heads. Such thermal printers are generally designed to applywater based inks with a viscosity of 2-5 centipoise (cps)

Recently large-scale thermal print heads with a printable width of 223mm and with a printing speed of about 20 m/min or more have beendeveloped by Memjet. The print head contains 5 ink channels and two rowsof nozzles per channel. Each individual nozzle structure is about30-microns across, enabling 800 dpi, with the second row of nozzles foreach colour slightly offset from the first to deliver 1600 dpi incombination. A Memjet print head can continuously fire up to 750 million2 picolitres drops with a 14 micron drop diameter per second. The printhead cost is less than 10% of the costs for conventional Piezo headswith similar capacity. Such thermal printers may apply water basedsubstances with a viscosity of 0.7-1.5 centipoise which is similar towater viscosity (1 centipoise at 20° C.). The Memjet print headcomprises a self-cooling system with the heating element in the middleof the ink chamber. As drops are ejected, new ink flows into the chamberand cools the heating element.

Thermal technology imposes the limitation that the ink must beheat-resistant, generally up to 300° C. because the firing process isheat-based. This makes it very difficult to produce pigment based multicolour thermal heads. The Memjet print heads are designed for dye basedink and are therefore not used in the flooring industry and inindustrial applications where high quality pigment based inks arerequired.

Most commercial and industrial inkjet printers and some consumerprinters use the piezoelectric printer head technology, which is themajor technology used in the flooring industry. A piezoelectric crystalmaterial (generally called Piezo) in an ink-filled chamber behind eachnozzle is used instead of a heating element. When a voltage is applied,the piezoelectric material changes shape, which generates a pressurepulse in the fluid forcing a droplet of ink from the nozzle. A Piezoprint head configuration may use different basic deformation principlesto eject drops from a nozzle. These principles are generally classifiedin squeeze, bend, push and shear print head technologies. Apiezoelectric crystal may also be used to create acoustic waves as itvibrates and to cause the ink to break into droplets at regularintervals. Piezo inkjet allows a wider variety of inks and higherviscosity than thermal inkjet. The ink has generally a viscosity in therange of 2-12 centipoise and is very suitable to apply pigment basedink. In industrial applications print heads that may handle highviscosity inks are often used since the initial viscosity of the inkdecreases considerably during production when temperature may increaseto 40° C. or more and a low initial viscosity may fall below the minimumlevel that is required for a proper functioning of the print head.

FIG. 1e shows how ink drops 56 are ejected according to the bend mode ofpiezoelectric material. A Piezo print head 30 comprises arrays of verysmall holes generally called jets 50 from which droplets 56 of ink 58,with pigments 12, are ejected on a paper surface.

The ink 58 flows from an ink container via an ink inlet 55 into an inkchamber 52. Electrical pulses bend a Piezo crystal 51 and a membrane 53.This deformation creates a pressure pulse that ejects an ink drop 56from the nozzle 54. Different drop sizes may be formed by varying theelectrical charge. The nozzles are typically about 10 microns indiameter. Typical drop volumes are in the range of 2-5 picolitersproducing printed ink spot sizes 57 on a surface in the range of 10-20microns. Each droplet may contain about 20% pigments. The remaining partis a liquid carrier and resins needed to connect the pigments to thesurface.

A digital image contains a grid of a fixed number of rows and columns ofpixels, which are the smallest individual element in a digital image.The grid is called a raster. The pixels, which represent images as acomputer file, are of a uniform size and shape. They do not overlap andthey touch adjacent pixels on all sides. Raster images can be created bya variety of input devices, for example, a digital camera. All knownprinters use a Raster Image Processing (RIP) software, which takes animage file input and produces a colour profiled, screened, bitmap outputthat controls the print heads and provides the necessary data that isneeded to apply an ink drop on a surface in a pre-determined rasterpattern R1-R4 as shown in FIG. 1 e.

A lot of ink types may be used. The main components are colourants thatprovide the colour, a binder that bonds the colourants to the surfaceand a liquid carrier that transfers the colorant and the binder from theprint head in well-defined small drops to a surface with a non-contactapplication method. The colourant is either a dye or pigment or acombination of both. The carrier fluid may be water-based or solventbased. The carrier fluid evaporates and leaves the colourant on thesurface. UV curable inks are similar to solvent based inks but thecarrier fluid cures when exposed to strong UV light.

A main problem for all types of inks and print heads is that when inkdries by evaporation it may dry up and clog the nozzles. Industrialprinters may be equipped with an ink circulation system that circulatesthe ink through the jets in order to increase the so called “decap” timewhich is the amount of time a print head can be left uncapped and idleand still fire ink drops properly. A short decap time or clogging mayresults in permanent nozzle loss and undesired lines may be formed overthe whole surface when single pass printers are used. Especiallypigment-based inks comprising polymer binders systems have a tendency todry out and it would be a major advantage if the decap time could beincreased and nozzle clogging could be avoided.

A dye is a colourant that is dissolved fully into the carrier fluid andthe ink is a true solution. Pigments are very fine powder of solidcolourant particles that are suspended or dispersed throughout a liquidcarrier. Pigment based inks are generally individually mixed together byusing colour pigments and several chemicals. Pigments used in digitalink are very small and have an average particle size of about 0.1micron. The common size of the nozzles is about 10-20 microns, whichmeans that the pigment particles have enough space to pass through thenozzle channels in the print head. The nozzles may still be blocked bythe ink itself and pigments that form clusters of particles. Highquality pigment ink should keep the pigment suspended in the carrierfluid for a long period of time. This is difficult particularly at therather low viscosities, which are required for a good functioning of theprint heads. Pigments have a natural tendency to settle out and falldown in the liquid carrier. In high quality pigment ink, no settling outof the pigment should normally occur. Advanced ink circulation systemsare used to avoid such problems related to ink with high pigmentcontent.

Pigment inks are generally more light stable, especially when exposed toUV light, and more fade resistant than dye-based inks. They aretherefore used in almost all flooring applications. Water based digitalinks comprising colour pigments are especially suitable for flooringapplications and may provide a high quality printing method in manydifferent materials.

Generally the pigments do not stick to a smooth surface. They aresimilar to sand particles and may be easily removed from most dry andsmooth surfaces. The water based carrier fluid is therefore generallymixed with small amounts of several other additives to provide specialink and print properties such as binders that provide the adhesion ofthe pigments to a surface, dot gain, pH level, drop formation, corrosionof the print head, fade resistance, etc. The inclusion of resins thatserve as binder in the ink composition limits the possible amount ofpigments, as both components increases the ink viscosity.

Colour pigments as raw materials are rather cost competitive especiallyas rather large particles of about one micron but the production ofpigment based inks comprising very small particles and other inks fordigital printers is very complicated and expensive and this results in avery high cost for the ink that normally may be in the region of about50-100 EUR/litre. About 50-100 m² of flooring may be printed with onelitre (20-10 g/m²) if a full high quality print is applied and thisgives a printing cost of 1-2 EUR/m². The costs for a conventionalprinted floor surfaces where printing cylinders are used are only 10% ofthe cost for digitally printed floor surfaces. This means that digitalprinting based on conventional pigment based liquid ink is only costcompetitive in small series when very high production flexibility isrequired.

Digital ink jet printers use a non-contact method to apply the ink on asurface. Laser printing however is based on a contact method where alaser beam projects an image on an electrically charged rotating drum,generally called photo conductor drum. Dry ink particles, generallycalled toner, are then electrostatically picked up by the drum's chargedareas. The ink comprises fine and very well defined spherical particlesof dry plastic powder such as, for example, styrene acrylate copolymeror polyester resin which is mixed with carbon black or colouring agents.The particles have a diameter of about 8-10 microns when 600 DPIprinting resolution is required. Some laser printers use even smallerparticles with a diameter of about 5 microns. The thermosetting plasticmaterial acts as a binder. The drum prints the image on a paper bydirect contact and heat, which fuses the ink to the paper by bonding theplastic powder to the paper. Colour laser printers use the CMYKprinciple with coloured dry ink, typically cyan, magenta, yellow, andblack that are mixed in order to provide a high quality coloured image.

The laser technology with the impact method is not used for printing ofa flat panel surfaces such as a floor panel surfaces.

3D printing is a well-known technology that is used to apply and connectseveral layers of liquid substance, powder or foils on each other inorder to create advanced three dimensional structures. The technology ismainly used for prototype production of small complex products. Severalhundred layers may be applied on each other. Several principles are usedto build layered structures. According to one main principle powderlayers are applied on each other and some parts are bonded by a liquidUV cured substance applied by a digital print head on each powder layer.Non-bonded powder is removed when the whole structure of the product isformed. Another principle uses a small glue gun that applies severallayers of hot liquid plastic material in several layers. 3D printershave a very low productivity and construction of even small objects cantake several hours. 3D printers are not used to create flat décors on asurface where colourants are applied side by side and where non-bondedpowder must be removed after each application of a layer. The structureof the layers applied on each other will be destroyed if pressing isused to cure the layers.

Dye-sublimation printers use a long roll of transparent film of red,blue, yellow, and grey coloured cellophane sheets that are attachedtogether end to end. Embedded in this film of many sheets attached toeach other are solid dyes corresponding to the four basic colours cyan,magenta, yellow and black and each sheet comprises only one colour. The“print head” contains thousands of small heating elements that producevarying amounts of heat and the dye is transferred to a coated paperwith “sublimation” which means that the dye when heated turns into a gaswithout first turning into a liquid. Such thermal print heads, hereafterreferred to as heating print heads in order to differentiate such headsagainst the thermal print heads used in bubble jet printing, heats up asit passes over the film, causing the dyes to vaporize before they returnto solid form on the paper. This method eliminates the used of liquidink and may provide a high photo quality with dyes that are transparentand that blend into a continuous-tone colour. However, the method hasmany disadvantages. Each sheet must have the same size as the printedsurface and the whole sheet is used even if a small part of the surfaceis printed with a specific colour. In order to eliminate some of thedisadvantages dye sublimation heat transfer imprinting printers havebeen developed, which use special inks comprising sublimation particles.A conventional inkjet printer may be used to print an image with suchsublimation ink on a special paper or foil. The image is thereaftertransferred by pressure and heat to a polyester material or a surfacethat has a polymer coating.

Thermal printing with heating print heads are also used to createdigital prints directly on a heat sensitive paper or indirectly with athermal transfer printing method where the heat is applied on a heatsensitive transfer film. These printing methods are mainly used to applyone colour on a paper and to print, for example, labels. The heatingprint heads have several advantages. They are reliable since there areno risks for clogging of inks and the price is cost competitive. Themajor disadvantages are related to high cost for the paper or transferfilm and the colour limitations to mainly one colour. Heating printheads are available in widths of up to 200 mm and may provide aresolution of up to 600 DPI.

Digital printing is a very flexible method that may provide a highquality print but it cannot be fully utilized in industrial applicationand especially not in floorings due to the high cost for the ink,problems related to drying and clogging of nozzles, especially whenpigment based inks are used and the need for special protective layersthat are costly and not completely transparent. The high ink costs areprimarily caused by the need to mill down the colour pigments towell-defined very small particles and to disperse the particlesthroughout the carrier fluid. It would be a major advantage if digitalimages may be created with colour pigments that may be larger, that arenot dispersed in a carrier fluid and that are not applied as drops bysmall nozzles. It would also be a major advantage if digital images maybe formed with higher wear resistance and without protective layers.

The majority of all the above-described floors and especially digitallyprinted floors have an embossed surface structure, especially when thedecorative printed décor is a wood pattern. The embossed structure wasin the past provided as a separate general structure that was used formany different décor types. Recently most floor producers haveintroduced the so-called Embossed In Register EIR method where theembossed surface structure is specifically formed for each type of woodspecies and the embossing is made in register with the printed décor.This provides advanced designs that are difficult to differential fromthe natural materials such as wood and stone. The embossing is obtainedwhen the surface is pressed against a structured matrix that may be asteal plate, steal belt, metal roller, plastic foil or coated paper. Thedécor must be positioned with high precision against the pressingmatrix. Generally digital cameras and mechanical devices that adjust thefinal position of the panel such that it matches the décor beforepressing are used to obtain such positioning. One specific problemrelated to laminate flooring is the fact that the printed-paper swellsand shrinks in an uncontrolled way during impregnation and the size ofthe décor may vary between different impregnate paper sheets.

The flexibility of digital printing is also limited in connection withEIR surfaces since the printed décor must always be adapted to theembossed matrix. A common feature for all such floors as described aboveis that all surfaces in a production batch have the same basic structureand are not possible to adjust and adapt to any changes in the décor.This repetition effect of the embossed structure provides a floorsurface that is not similar to a wood floor where practically all panelshave different designs and structures due to the wood grain structure ofthe wood. Copies of stone and other natural materials cannot be producedin a way that is a true copy of the natural material where design andstructure generally is perfectly combined and all panels are different.

The digital ink jet technology is mainly used to obtain advantagesrelated to the possibility to create a high-resolution image in aflexible way. However, the other aspects of the technology, mainlyrelated to the possibility to apply a liquid substance very preciselywith a non-impact method, have not been fully utilized or developed,especially not in applications where a décor is applied on a large sizepanel comprising a surface that during production and especially afterprinting receives it final shape and properties in production stepscomprising high pressure and heat.

It is known that powder applied on a liquid substance could be used tocreate raised portions or an image on mainly a paper substrate and thatthe liquid substance may be applied digitally by ink jet. 3-D printingcomprising several powder layers that are locally connected with adigital device such as an ink head and where excessive non-connectedpowder particles are removed in a final step is a well-known technologythat may be used to create an embossed structure on a panel. It is alsoknown that powder particles may be applied directly with a non-contactmethod on a surface comprising a binder or indirectly with a contactmethod where a transfer method is used. Even combinations are knownwhere a non-contact transfer method is used and the powder is detachedfrom the transfer surface with heat or scraping.

U.S. Pat. No. 3,083,116 describes raised printing powder and a raisedprinting process comprising dusting a powdered resin upon a newlyprinted sheet, removing therefrom the excess powder which do not adhereto the wet ink, and applying heat to the powder retained on the sheet tofuse it so that particles thereof will flow together and adhere to thesheet. The powder may comprise a phenolic resin such as phenol, urea andmelamine.

U.S. Pat. No. 3,440,076 describes a method of forming raised hardprinted characters on a sheet of paper. An ink composition is printed onthe paper and then contacted with a dry material. One of the inkcomposition and dry material contains a thermosetting resin and theother material a blowing agent and a curing agent. The dry powdermaterial not adhering to the ink is removed and the resin associatedwith the printed character is then cured with heat at temperaturessufficient to fuse the powder.

U.S. Pat. No. 3,446,184 describes a method to form a sticky image copy.Toner powder is applied on a liquid forming and a portion of the powderis retained by the liquid coating, forming a visible image. Loose powderis removed and the sheet passes a heating unit where the retained powderis fused to form a permanent image.

U.S. Pat. No. 4,312,268 describes a method by which a water-based ink isapplied digitally to a continuous web and fusible single colour powdermaterial is applied to the web and on the ink. Some of the powdermaterial is bonded to the liquid, and non-bonded powder material isremoved from the web prior to heating of the web to dry the liquid andto fuse the powder material to the web by melting the powder. It ismentioned that the powder material may have a particle size in the rangeof 5 to 1000 microns and may have a melting point or fusing point in therange of 50 to 300° C. The powder material may be produced by dissolvingor dispersing, respectively, a dye or a pigment in a resin or resinformulation, followed by grinding, spray chilling or the like to reducethe material to a fine powder. The powder material may provide abrasionresistant qualities to the ink that may contain phenolic resin. Theliquid material, which is applied through the jets, may be clear andcolourless water.

GB 2 128 898 describes a method to form raised decorative portions in aplastic tile. A decorative floor covering in tile form has a designprinted on its upper surface. Particles such as inorganic sand particlesare positioned on the upper surface of a plastic tile with at least someof the particles being placed on the tile surface in register with thedesign printed on the tile surface. Excess sand particles are removed. Acured wear layer overlies both the raised particle and the plastic base,whereby the wear layer surface in the areas containing particles and inthe areas not containing particles will be of different glosscharacteristics. The process requires the sprinkling of particles overan adhesive coated surface to retain the particles in registration witha printed design on the tile surface.

U.S. Pat. No. 6,387,457 describes a method of using dry pigments forprinting applications related to automobile painting, security printing,general painting and cosmetics. A binder material is applied to asurface of a substrate uniformly or in a pattern. The binder is appliedby ink jet, spraying, screen, off-set or gravure printing. Dry pigmentis applied to the binder material in a pattern or uniformly. The drypigment material comprises flakes of non-metallic material having aparticle size less than about 100 micron. The flakes are aligned in adirection parallel with the surface of the substrate and a protectivecoating may be applied on the flakes.

EP 0 403 264 A2 describes a transfer method to form a multi-colour imageon a drum that transfers the image to a paper. A fluid digital latentimage is subsequently developed at a development station where colouredpowder is applied to the fluent latent image and fixed to produce avisible and permanent image. Several digital print heads may be usedthat print with dyeless fluids comprising a mixture of water withpolyhydric alcohols and their sub-sets of ethylene glycol, glycerol,diethylene glycol and polyethylene glycol. A powder toner is appliedacross the surface of the paper and a voltage is applied during thisdevelopment. The voltage is then reversed to remove the toner from thebackground areas. Fixing is achieved by means of conventional copierfusing methods.

U.S. Pat. No. 5,627,578 describes a method to produce raised letteringand graphics in desktop printing applications by using thermographicpowder and an ink jet printer to apply a liquid binder. The method issimilar to the above described methods to produce raised text.

EP 0 657 309 A1 describes a multicolour transfer method utilizing atransfer paper carrying a pattern formed by ink jet and powder similarto the above described methods. The transfer method is intended fordecorating ceramics.

WO 2007/096746 relates to systems and apparatuses for transferringgranular material with a non-contact or contact method to a surface tobe decorated, particularly for obtaining decorations on ceramic tiles. Aliquid digital pattern is provided by ink jet on a transferring surfacethat may be a drum or a belt. The granular material is applied andbonded to the transferring surface and only bonded granulate material ismoved to a transferring zone where heat is applied on one specificportion of the transferring surface in the transferring zone in order todetach the granular material from the transfer surface and to apply thegranular material on the receiving surface. The granules may also bedetached by scraping. The major advantage with this method is that onlyparticles that form the final image are applied on the receivingsurface. The major disadvantage is that heating must be sudden and theparticles must be released from the transferring zone and they must falldown on the receiving surface in a very controlled way in order toobtain a high resolution image. High resolution can only be obtainedwith rather heavy particles that fall by gravity on the receivingsurface. The granular material used in the invention is of the typecomprising non-porous granules, such as, for example, grits of vitreousmaterials or sintered mixtures, sands etc. in the various ranges ofgranulometry from 30 μm to 800 μm, preferably ranging from 50 μm to 150μm. A transfer print with a contact method is also described.

WO 2011/107610 describes a method to create an elevation or an embossingon a floor panel in order to avoid the use of expensive press plates.The method is the same as the known methods to create a raised print. Itdescribes a method to produce a floorboard by printing a curablesubstance for creating an elevation on the panel. The elevation may beapplied on a basic decorative pattern that is directly printed orlaminated on the panel. The curable substance may comprise wearresistant particles. The curable substance may be digitally printed onthe panel by first printing a liquid in a pre-defined pattern and thenproviding an intermediate substance that may comprise a powder. Thecurable substance may be cured by UV radiation or may be a varnish.

EP 2 213 476 A1 describes that a pre-determined pattern may be digitallyprinted on a carrier with curable liquid so as to form an embossingdecoration pattern, which is pressed on the overlay. The curable liquidmay be a plastic, which becomes rather rigid after curing, for example,a plastic containing ink. This method is not suitable for floorapplications. The digital printing head can only print a very thin layerwith a thickness of about 10-20 micron. Thicknesses of at least 100-200micron that are required to form an embossing in laminate and 200-700micron to match the requirement of powder based floors are not possibleto produce in an economic way.

WO 2012007230 describes a method to form a 3-D structure on a furnitureor floor panel with a digitally controllable device. A décor is appliedwith a flat three-dimensional structure of powder based coating materialcomprising one or more layers, which are locally solidified by adigitally controllable device under the action of light and or heatradiation. Excess non-solidified coating material is removed in a finalproduction step. The three dimensional structure may be digitallyprinted. A liquid coating material is applied on the 3-D structure as aprotective layer.

The majority of the known methods are based on direct application ofpowder on a surface comprising a binder pattern. They are mainly used tocreate raised text or three-dimensional decors, which are cured andprotected by a liquid coating. Such methods are not suitable forapplication where the coloured powder must be incorporated into thesurface in order to provide sufficient wear resistance. None of thesedirect application methods are combined with a pressing step thatcompresses the applied powder and especially not with a pressing stepthat cures the whole surface layer such that the powder particles arecured or fused into the surface.

Dye-sublimation printers with heating print heads use special colouredfilms and are not suitable to produce surfaces with high wear resistancesuch as floor surfaces. Heating print heads are no used to bond powderthat is applied on a surface, especially not on a panel surface.

The known methods are not suitable for creating a high qualitymulti-colour image on a building panel, and especially not on a floorpanel where UV resistant pigments must be used and where the image mustbe incorporated into a wear resistant surface. It is not known thatabove describe principles may be used to create a digital image on apanel that after the printing step is cured under high heat and pressureand especially not how the known principles should be adapted forprinting of floor surfaces similar to laminate and Wood Fibre Floors(WFF) where the powder, the ink and the application methods must beadapted to the specific thermosetting resins, wood fibre materials andpressing parameters which are needed to form a wear, impact and stainresistant high quality multi-colour surface in a cost efficient way.

The above description of various known aspects is the applicants'characterization of such, and is not an admission that the abovedescription is prior art when the described products, methods andequipment are used partly or completely in various combinations.

Objects and Summary

The main objective of at least certain embodiments of the invention isto provide an improved and cost efficient printing method to applycolourants on a surface in well-defined patterns on preferably a floorpanel surface by using digital technology.

A specific objective is to provide a method wherein heating print headsthat contain a large number of small heating elements that producevarying amounts of heat may be used.

The above objectives are exemplary, and the embodiments of the inventionmay accomplish different or additional embodiments.

Embodiments of the invention is based on a main principle whereconventional digital printing methods are divided in separate steps.Coloured particles are applied on a surface. Some particles are bondedby a digital heating print head. Other non-bonded particles are removedand the remaining bonded particles form a digital pattern. This processmay be repeated and several colours may be applied such that an advancedmulti colour high definition digital print may be formed. The colouredparticles may be pigment coated wood fibres or mineral particles andvery realistic copies of wood and stone designs may be obtained withsuch decorative materials arranged in advanced high quality patterns.The bonded coloured particles and the panel surface are pressed togetherand an increased bonding is obtained. The pressing is made underincreased temperature such that the coloured particles and the surfaceare cured to a hard wear resistant layer.

An advantage compared to conventional digital ink jet printing are thatthe coloured particles are not dispersed in a liquid substance and arenot applied by a digital printing head on a surface. Pigment basedcolourants may be combined with very cost effective and reliable heatingprint heads where no liquid inks are used that may evaporate and clogthe nozzles.

An advantage compared to known Dye-sublimation printers with heatingprint heads is that no special coloured films have to be used.Colourants and binders may be adapted to specific requirements that mustbe met in order to produce surfaces with high wear resistance such asfloor surfaces.

A first aspect of the invention is a method of forming a digital printon a surface, wherein the method comprises:

-   -   applying a powder of dry ink, the dry ink comprising colourants,        on the surface;    -   bonding a part of the powder of dry ink to the surface by a        digital heating print head such that the digital print is formed        by the bonded colourants of the dry ink; and    -   removing non-bonded dry ink from the surface.

The dry ink may comprise a heat sensitive resin.

The surface may comprise a heat sensitive resin.

The heat sensitive resin may be a thermosetting or thermoplastic resin.

The heat sensitive resin may be a thermosetting resin comprisingmelamine.

The digital heating print head may apply heat on a heat transfer foilthat is in contact with the digital heating print head and the dry inkparticles.

The heat transfer foil may comprise copper or aluminium.

The surface may be a part of a building panel.

The dry ink may comprise mineral particles.

The dry ink may comprise aluminium oxide particles.

The heat transfer foil may comprise individual small elements with highthermal conductivity.

The dry ink may comprise wood fibres.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will in the following be described in connection topreferred embodiments and in greater detail with reference to theappended exemplary drawings, wherein,

FIGS. 1a-e Illustrate know methods to produce a printed and embossedsurface;

FIGS. 2a-e Illustrate a first principle of an embodiment of theinvention;

FIGS. 3a-d Illustrate a second principle of an embodiment of theinvention;

FIGS. 4a-d Illustrate a third principle of an embodiment of theinvention;

FIGS. 5a-h Illustrate digital application of pigments according to thefirst principle of an embodiment of the invention;

FIGS. 6a-d Illustrate production methods based on the first principle ofan embodiment of the invention and a panel with a decorative patternformed according to an embodiment of the invention;

FIGS. 7a-c Illustrate application of colourants on a surface;

FIGS. 8a-h Illustrate preferred embodiments of macro colourants;

FIGS. 9a-e Illustrate application and pressing of macro colourants;

FIGS. 10a-c Illustrate application and pressing of macro colourants;

FIGS. 11a-c Illustrate application of several colours with one printhead and application and removal of colourants with intermediatepre-pressing;

FIGS. 12a-d Illustrate transfer printing methods and panels withpreferred surfaces;

FIGS. 13a-d Illustrate application of colourants in patterns withmethods where liquid blank ink is not used to bond colourants;

FIGS. 14a-d Illustrate digital embossing with press particles; and

FIGS. 15a-d Illustrate digital embossing combined with digital transferprint.

DETAILED DESCRIPTION OF EMBODIMENTS

The methods that are used to provide a digital print with heating printheads are in this disclosure based on similar technologies that are usedto bond powder with thermal digital ink jet print heads. A detaileddescription of the liquid bonding methods are therefore included. Thedigital technologies that are based on liquid bonding, heat bonding andconventional ink jet printing may be combined and a panel may forexample comprise several colours formed by a combination of such digitalprinting technologies.

FIGS. 2a-2d show schematically an embodiment of the invention, which isbased on a first principle where a binder pattern BP or image is formeddigitally by an ink head that preferably only applies a binder 11 on asurface 2 as shown in FIG. 2a . Colourants 7, that may comprise smallcoloured particles, for example, pigments 12, are applied randomlypreferably in dry form by a second device such that they are in contactwith the binder pattern BP. FIG. 2b shows a preferred embodiment wherepigments 12 in dry form are scattered over the binder pattern BP. FIG.2c shows that the binder 11 connects some pigments 12 that form the samepattern as the binder 11 and a print P is formed on the surface 2 whenother non-bonded pigments 12 are removed from the surface 2 by, forexample, vacuum.

This three-step process, hereafter referred to as “print forming cycle”,when the process relates to a one colour application, or “Binder AndPowder printing”, or BAP printing, when the process refers to the wholeprint and where preferably a liquid binder 11, hereafter referred to as“blank ink” and dry particles comprising colourants 7, hereafterreferred to as “dry ink” 15, are applied separately and bonded togetherand where non-bonded particles are removed, may provide a digital printP with the same or even superior quality as conventional digitalprinting technology.

The surface 2 may be a paper layer or a foil or a powder layer.

The surface 2 may be a part of a building panel or a floor panel 1.

The binder may be blank ink 11 comprising a liquid substance that ispreferably applied by a digital ink head.

The liquid substance may be water based.

The surface 2 with the bonded colourants 7 may be heated and pressed.

The surface 2 and the colourants 7 may be pressed and cured to a hardsurface with an embossed structure.

The colourants 7 may be macro colourant particles larger than 20 micronsand they may be pressed into the surface 2.

The surface 2 may be a part of a panel 1 that may be a laminate or woodfloor, a powder based floor, a tile or a LVT floor.

The liquid blank ink may be replaced with a digital heating processwhere heat from a digital heating print head or a laser activates abinder included in the dry ink and/or in the surface.

The blank ink and the dry ink may be applied in many alternative ways.The surface 2 may point upwards or downwards and the blank and/or thedry ink may be applied from above or from below. A surface 2 with blankink may, for example, point downwards and may be brought into contactwith a dry ink layer. Non-bonded dry ink may be removed by gravity whenthe surface is separated from the dry ink layer. In order to simplifythe description, the majority of the preferred embodiments show asurface pointing upwards and attached to a panel prior to printing.Separate surfaces 2 without a supporting panel 1 may be printedaccording to the principles of the invention.

The method is particularly suitable in applications where considerablequantities of colourants, preferably pigments, are applied on a largeflat panel in order to form an advanced large print or decorativepattern with preferably high wear, impact and UV resistance and wherethe pattern preferably is intended to copy a wood or stone design. Suchdesigns are generally formed with one base colour that, for example,gives the wood or the stone the basic appearance and a few spot coloursthat are used to form the wood grain structure, knots, cracks andvarious defect which are visible in the wood surface or crystalstructures cracks and other defects in a stone design. The method isalso very suitable to form a pattern on a tile or to print laminate andpowder based floors with a copy of, for example, a tile floor thatcomprises tiles with different colours and grout lines between thetiles.

Contrary to known methods, the digital ink head, hereafter referred toas “digital drop application head” 30′, is not used to apply any type ofconventional ink with colour pigments or dyes. This is an advantagesince no expensive inks comprising pigment dispersions and binder resinshave to be handled by the digital drop application head 30′.

The blank ink is preferably an essentially transparent liquid substancethat preferably mainly comprises water.

The blank ink, also called liquid substance, comprises preferably nopigments.

A print provided by the blank ink or liquid substance may be referred toas a liquid print P. The liquid print may be formed of drops of theblank ink applied on the surface.

The colourants are preferably bonded to the surface in two steps. Thefirst bonding is an application bonding where the bonding of thecolourants should be sufficient to keep the colourants connected to thebinder pattern BP in order to allow the remaining excessive colourantsthat have been applied on areas outside the binder pattern, to beremoved.

The second bonding is a permanent bonding intended to connectpermanently the application-bonded colourants to the surface 2.

The first application bond and the second permanent bond may comprise anintermediate stabilization step where the structure of the bondedcolourants are modified by, for example, heat and/or pressure such thata new print forming cycle may be made. The intermediate stabilizationstep allows that the new non-bonded colourants that are applied on thesurface during a second print forming cycle may be easily removed evenon surface parts that comprise colourants from the first print formingcycle.

The first application bonding is preferably obtained with a liquidsubstance, also referred to as blank ink, that preferably mainlycomprises distilled or deionized water. The adhesion of water may insome application, especially when only one colour is applied, connectthe colourant to the surface with a force that is sufficient to allowremoval of the non-bonded colourants. The production costs for such aliquid substance are extremely low and clogging of the nozzles when abinder dries may be avoided. Some chemicals may be added, for exampleglycol or glycerine, that are needed to reach the viscosity and surfacetension of the liquid substance that may be needed for a proper functionof a print head. Water-soluble polyethylene glycol (PEG), that isavailable in many different molecular weights, is especially suitable tomodify water such that a blank ink with an appropriate viscosity thatworks, for example, with Piezo heads may be obtained. Low monocularweight formulations such as, for example, PEG 400 are especiallysuitable to use in blank ink and preferably together with dry ink or asurface that comprises thermosetting resins such as melamine. Water andPEG are compatible with melamine resins and allows easy and fast curingwhen heat and preferably also pressure is applied. A preferred nondryingsolvent that is compatible with thermosetting resins should be misciblewith water, have a boiling point above 100° C. and a melting point lowerthan the application temperature. Examples of such, but not restrictedto, are ethylene glycol, propylene glycol, polyethylene glycol,diethylene glycol, butane diol and glycerine. Combinations can also beused. In some applications some other minor amounts of chemicals may beincluded in the blank ink, for example, wetting agents and otherchemicals that are needed to prevent bleeding when the blank ink isapplied on a surface. The blank ink may also comprise release agents,especially when a direct application of the colourants, hereafterreferred to as “direct BAP printing” as described above is replaced by atransfer application hereafter referred to as “transfer BAP printing”where the blank ink and colourants are in a first step applied on atransfer surface and then pressed against and bonded to the surface.Most such additives are cost efficient and the blank ink may have aproduction cost which is a fraction of the costs for conventionalpigment based inks.

Most Piezo print heads are designed to work with a viscosity in therange of 2 to 12 centipoise (cps). The water based blank ink may easilybe adapted to meet all possible viscosity requirements.

A suitable blank ink that preferably may be used in a low viscosityprint head designed to operate with a viscosity of about 5 cps such as aKyocera print head may be a water based glycol solution comprising, forexample, about 75% (weight) Ethylene Glycol or 55% Diethylene Glycol or50% Propylene Glycol or 38% Polyethylene Glycol PEG 400. A water basedglycerine solution comprising about 40% glycerine may also be used.De-ionized water may also be mixed with Glycerine and Glycol. A suitableblank ink for a low viscosity print head may, for example, compriseabout 40% water, 50% Glycerine and 10% Diethylene Glycol.

A suitable blank ink that preferably may be used in a high viscosityprint head designed to operate with a viscosity of about 10-12 cps suchas a Fuji print head may be a water based Glycol solution comprising,for example, about 95% (weight) Ethylene Glycol or 75% Diethylene Glycolor 70% Propylene Glycol or 50% Polyethylene Glycol PEG 400. A waterbased Glycerine solution comprising about 65% glycerine may also beused. De-ionized water may also be mixed with Glycerine and Glycol. Asuitable blank ink for a high viscosity print head may, for example,comprise about 30% water, 60% Glycerine and 10% Diethylene Glycol.

The water content for blank ink adapted for low and high viscosity Piezoprint heads may be increased further if high viscosity glycols are used;for example, Polyethylene Glycol with a higher molecular weight than PEG400. A preferred blank ink that preferably is suitable for Piezo printheads may comprise 0-70% water and 30-100% Glycol and/or Glycerine. Evenmore preferred is a formulation comprising 10-70% water and 30-90%Glycol and/or Glycerine. Blank ink that is suitable for thermal bubblejet print heads that are designed for very low viscosities; for example,2-4 cps may comprise more than 70% water.

All blank ink formulations may comprise small amounts, about 1%, ofwetting agents such as BYK or Surfinol and chemicals such as Actidiceintended for control of bacteria and fungi.

The blank ink is preferably essentially a non-curable liquid substancethat is used to obtain the application bonding and to bond the colorantsuntil the final permanent bonding takes place preferably with heat andpressure and with resins that are a part of the substrate materialand/or the dry ink particles. Such blank ink will not bond particleswhen it dries or when heat is applied.

The blank ink may comprise special curable binders, preferably waterbased acrylic emulsions, which are compatible with water, glycol orglycerine. Preferable binder content is 5-20%. Acrylic emulsions willbond particles when the water content evaporates and they will create astrong bond under high heat and pressure.

A high water content of at least 50% gives the advantages that thematerial cost may be low. The decap time will be rather short, less thanone hour, since water evaporates. A low water content combined with ahigh glycol or glycerine content will increase the decap timeconsiderably. Blank ink with a water content below 40% may have a decaptime of several hours. Water content below 20% will give a very longdecap time that may exceed 6 hours. It is possible to use blank ink thatcomprises more than 90% glycol and this may increase the decap time toseveral days. Blank ink may be made without water and high viscosityprint heads may handle blank ink that comprises, for example, 100%Ethylene Glycol.

An ink circulation system may be avoided in industrial printers whenblank ink is used that does not comprise any pigment dispersions orbinders and that is mainly a water based solution as described above.This will decrease the cost for the printing equipment considerably.

FIG. 2e shows viscosity in cps of aqueous Propylene Glycol (PG)solutions in temperatures 20-30° C. W1 shows viscosity of water. Pg1comprises 50% PG and 50% water. Pg2 comprises 70% PG and 30% water.Viscosity of blank ink adapted for a low viscosity print head may varybetween 4-6 cps within the temperature range of 20-30° C. The viscosityof blank ink adapted to high viscosity print heads may vary between 8-14cps and this may be outside the normal working conditions of the printhead. This problem may be solved with printing equipment that comprisesa temperature control system that preferably is combined with a climatecontrol system that controls the humidity. Decap time for water basedblank ink may be increased if the relative humidity around the printheads is above 50%.

The binder that bonds the colourants to the surface may comprise twocomponents. The first binder component may be included in the blank ink.The second binder component may be included in the dry ink or thesurface and activated by the blank ink. This makes it possible to use,for example, water in order to obtain the application bonding,stabilization and permanent bonding. Water may react with a binder thatmay be included in the colourants or in the surface. The blank ink mayof course comprise a binder that may provide the same bonding as the twocomponents mentioned above.

The blank ink may be applied on any surface 2, for example, anon-transparent paper layer, an essentially transparent overlay, apowder layer, a stabilized powder layer, a wood veneer or wood sheet, atile glazing, a plastic foil or a base colour applied on a sheet shapedmaterial preferably comprising wood or polymer material.

The application of the surface 2 to a sheet shaped material such as apanel 1 gives several advantages. Handling and positioning of looselayers that may swell and shrink during the application of liquid blankink may be avoided. The application bonding of the colourants 7 may bemade with a very low bonding strength since the surface 2 is supportedby the flat panel and may be displaced horizontally on a conveyordirectly into a press where the permanent bonding with heat and pressuretakes place. Rolling, cutting and stacking of paper and foil surfacesmay be avoided. Some surfaces such as uncured powder and tile glazingcannot be handled without a support of a panel 1.

BAP printing on LVT floors may also be made when, for example, theindividual base layers, preferably including a glass fibre layer, and adecorative plastic foil with a base colour are fused together to apanel. A transparent protective layer may be fused with heat andpressure on the BAP print and the decorative plastic foil such that thedry ink particles are permanently bonded and fused to the surface. Theblank ink may be adapted such that floating of the drops on the smoothplastic foil is avoided. It is an advantage if the blank ink has a highviscosity, preferably 10 cps and higher.

BAP printing on ceramic tiles is preferably made when the powder ispressed to a tile body forming a panel. A glazing with a preferably basecolour is applied on the tile and a BAP print is applied on the dryglazing. The BAP print and the tile body is thereafter pressed and aprotective transparent glazing is applied on the pressed print. The tileis after glazing fired in a furnace or kiln at very high temperaturessuch that the dry ink particles cure and melt into the tile body and theglazing.

Embodiments described above are based on the main principles that theBAP print is applied on a surface 2 that forms a part of a panel 1 andthat also comprises a material composition such that when heat andpressure is applied, the panel, the surface and the print will bepermanently bonded together. Such surfaces may comprise thermosettingresins, preferably melamine formaldehyde resins which generally are usedin WFF or paper based laminate floors, curable and fusible mineralmaterials used in ceramic tiles, or thermoplastic materials used in LVTfloors.

Direct and transfer BAP printing may also be used on textile surfaces.Dry ink and blank ink may be specially adapted for various textilesurfaces. Binders, dry ink viscosity and the size or the colourants maybe adapted to provide an appropriate bonding and removal of thecolourants.

Application on some specific surfaces may be improved by a so-calledcorona treatment, sometimes also referred to as air plasma. This is asurface modification technique that uses low temperature coronadischarged plasma to impart changes in the properties of a surface. Thecorona plasma is generated by the application of high voltage to sharpelectrode tips, which forms plasma at the ends of the sharp tips.Materials such as plastics, glass or paper may be passed through thecorona plasma curtain in order to change the surface energy of thematerial. The surface may also be treated with various types mineralsalts.

The surface may comprise a first base colour, which may be used tocreate a major part of the coloured visible surface. Powder basedsurfaces, preferably comprising thermosetting resins, may be pre-pressedand formed with a smooth surface that facilitates the application andremoval of the colourants. The pre-pressing is preferably made withpressure and heat and during a press cycle time that ensures that themelamine resin is in a semi-cured level and in an B stage as describedin the introduction.

The colourant comprises, in a preferred embodiment, mainly colourpigments 12 that are scattered as dry powder layer over the wet binderpattern BP as shown in FIG. 2b . The pigments may be mixed with otherparticles, for example, melamine powder particles 13 that melt when theyare in contact with the liquid binder pattern BP and that bond thepigments to the surface. The dry non-bonded pigments and melamine powder13 may be removed by, for example, an air stream or gravity and theremaining wet melamine 13 and colour pigments 12 form a print P as shownin FIG. 2c which is essentially identical to the binder pattern BPcreated by the blank ink. Dry ink may have the same material compositionas the surface layer 2 in a powder based WFF floor and may comprise amix of woof fibres, a dry melamine formaldehyde resin powder, aluminiumoxide particles and colour pigments.

The stabilization of the print may be partly or completely obtained by,for example, exposure to IR, hot air, UV lights, microwaves,pre-pressing or similar or combinations of such methods. The binder,that in this preferred embodiment is water or wet melamine, ispreferably stabilized by pre-pressing that bonds the colour pigments tothe surface 2 by drying the wet melamine or by melting the melamineparticles. The pre-pressing compresses the surface of the printedpattern P. A second pattern may be printed with the blank ink on thesurface 2 and a second layer of pigments and melamine powder may beapplied on the surface and over the first print. This may be repeatedand an advanced décor may be created with several colours such that thedigital image comprises colourants with different colours positionedhorizontally offset in the same plane.

The blank ink is preferably an essentially transparent liquid substancethat does not disturb the colour of the bonded colourants. Blank inkwith the same liquid substance may be used together with dry inkcomprising many different colourants and this allows that, for example,one print head with the same blank ink may be used to apply severaldifferent colours that may be applied in several steps with anintermediate application of a digital pattern formed by the blank ink.This allows that the number of print heads may be reduced considerablysince one print head with one ink channel applying the same blank inkmay be used to apply a practically unlimited number of dry inks withdifferent colours, structures particle sizes etc. The simple compositionof the blank ink makes it possible to use more cost efficient printheads since no colour pigments are fired through the small nozzles ofthe print head.

The stabilization step may in some applications be sufficient to createthe permanent bonding. The final permanent bonding may also take placewhen the surface preferably is pressed and cured under heat and pressureaccording to the methods that are used to cure a laminate or a powderbased surface comprising a thermosetting resin or a surface comprising athermoplastic layer. An UV curing transparent lacquer that is appliedover the colourants and that after application is cured in an UV ovenmay also be used. This transparent layer may be applied in liquid formby rollers or with digital Piezo heads and in one or several steps withintermediate UV curing. A thermoplastic resin or thermoplastic particlesmay also be used to obtain the first application bond or the secondpermanent bonding. Paper based or powder based overlay comprisingaluminium oxide and melamine resins may also be used as protectivelayers and as permanent bonding.

The low cost and the simple chemical composition of the liquid substanceapplied by the drop application head makes it possible to use rathersimple digital print head technology to apply the liquid bindersubstance. CIJ (continuous inkjet) may be used since water is easy torecycle and the collected drops may even be disposed without anyrecycling. Cost efficient thermal print heads may be used since water iseasy to handle with bubble jet technology. Rather simple Piezo headswith high productivity and with DOD (drop on demand) systems may be usedthat may have a long life time and that require a minimum of maintenancedue to the very favourable composition of the liquid substance that willnot cause any production disturbance since there are no pigments andpreferably no fast drying resins that must be handled, which is the casewhen conventional pigment based inks are used.

The binder may comprise a wide variety of thermosetting andthermoplastic materials that may be used as particles or chemicals inthe surface, in the dry ink or as dispersions in the blank ink appliedby the digital drop application head. The majority of such materials maybe produced in dry powder form or as liquid dispersions. It is preferredthat the chemical substance that provides the bonding after drying isincluded in the surface or in the dry ink and that the blank ink is asimple liquid chemical substance without any resins or other chemicalsthat in dry form may clog the nozzles.

As an alternative to thermosetting materials such as melamine or tothermoplastic materials such as, for example, PVC powder, UV curedpolyurethane may, for example, be used in powder form or as dispersion.

UV curable polyurethane substance with a viscosity that is adapted tothe digital drop application head 30′ may be used. Water-basedpolyurethane dispersions are preferred as a liquid substance in thedigital drop application head since they do not cure until they areexposed to UV light. Polyurethane dispersions are fully reactedpolyurethane/polyureas of small and discrete polymer particles and suchparticles may be produced with a size of about 0.01-5.0 microns and maytherefore be handled in a digital print head or other similar heads.Polyurethane dispersions may be blended with, for example, acrylicemulsions and other emulsions in order to reduce costs.

The digital drop application head, that in some applications preferablymay be a Piezo head, has preferably a capacity to fire drops with a dropsize of about 1-200 picolitres or more. The drop size and drop intensitymay be varied and this may be used to vary the intensity of a colour andto create a so-called “grey scale” with the same basic colour. Largerdrops will bond thicker layers of dry ink and smaller drops will bondthinner layers.

Water based adhesives may also be used such as soluble adhesives orwater dispersed adhesives.

Other UV cured materials such as acrylates of epoxy, urethane,polyester, polyether, amine modified polyether acrylic and miscellaneousacrylate oligomers may be used as binders in powder form or asdispersions.

The blank ink may also be applied on a surface by spray nozzles or byengraved rollers.

FIG. 2d shows schematically one BAP printing station 40 of a binderprinting equipment that may be used to create a digital print P on apanel 1 comprising a surface 2, a core 3, and a backing layer 4. A blankink application station 36 comprising a digital drop application head30′, that preferably is a Piezo head or a thermal print head, applies abinder pattern BP with blank ink 11. Several heads 30′ may be positionedside by side in order to cover the width of the surface that is printed.The binder pattern is created digitally in the same way as inconventional digital printing. The colours are separated and each blankink application station 36 applies mainly the same liquid substance orblank ink that is used to bond one specific colour in each print formingcycle. The digital drop application head is connected with a feedingpipe 32 to a container 31 with blank ink. The digital drop applicationheads 30′ are digitally connected with preferably data cables 33 orwireless to a digital control unit 34 that controls the application ofthe drops, the speed of the conveyor 21, the function of a dry inkapplication unit 27 and all other equipment that is used to bond andremove pigments.

The water based drops of the blank ink 11, which in this embodimentserve as an application binder, should be wet until they pass the dryink application station 27 that in this preferred embodiment is ascattering station. Dry ink 15, that in this preferred embodimentcomprises colourants of colour pigments 12 mixed with a resin of spraydried melamine powder 13, is scattered on the liquid blank ink 11.

The scattering equipment comprises a hopper 45 that contains dry ink 15,a doctor blade 47 that together with a roller 46, preferably comprisingan engraved, embossed, etched or sand blasted roller surface 44, acts asa dispensing device that moves a pre-determined amount of dry ink 15from the hopper 45 and to the surface 2. The roller 46 may also have aroller surface 44 that comprises small needles. Rotating and oscillatingrollers may also be used. A material-removing device that may be anoscillating or rotating brush 48 may also be used in some applicationstogether with one or several rotating or oscillating meshes 49 that mayoscillate or rotate in different directions.

The doctor blade 47 may be rigid or flexible and may have an edge thatis adapted to the structure of the roller surface. The oscillating orrotating meshes 49 may also be formed such that they spread the dry ink15 in a pre-defined way and they may be combined with one of severalnets that may be used to sieve the particles before they are applied asa layer. The rotation of the roller, the position of the doctor bladeand the speed of the surface that is intended to be covered with the dryink may be used to control the layer thickness.

The liquid blank ink 11 and the dry ink with pigments 12 and meltedmelamine particles 13 is in this embodiment heated and stabilized whenit is displaced under preferably a hot IR lamp 23, which is locatedpreferably after the digital drop application head 30′ in the feedingdirection.

A dry ink removal station 28, that in this embodiment is based on airstreams and vacuum, removes pigments 12 and melamine particles 13 thatare not wet and not bonded by the binder pattern BP and a perfect colourprint P is provided. The dry ink removal station may be located afterthe IR lights 23 or between the IR lights and the scattering station 27.This production step may be repeated and a second scattering station 27that comprises another colour may apply a second colour on a binderpattern that may be applied by the same print head or a new print headthat is used in a second print forming cycle. The removed dried pigmentsand melamine particles may pass through a sieve or a filter and they maybe recycled and reused again several times.

The panel 1 with the surface 2 is preferably displaced essentiallyhorizontally under the digital drop application head 30′, the dry inkapplication station 27 and the dry ink removal station 28 with one orseveral conveyors 21. It is obvious that the digital drop applicationhead 30′, the dry ink application station 27 and the dry ink removalstation 28 may alternatively be displaced over a panel 1 during the BAPprinting.

The dry ink may in addition to pigments and melamine particles alsocomprise wear resistant particles, such as small aluminium oxideparticles, and fibres, preferably wood fibres, that preferably maycomprise or consist of bleached transparent or semi-transparent fibres.Such dry ink may be used to create a solid print with pigments that arepositioned vertically above each other with binders and wear resistantparticles above and below the pigments. Small drops of blank ink may dueto capillarity and the combination of surface tension and adhesiveforces penetrate into the dry ink and bond larger amounts of dry inkthan an application with conventional ink where pigments are applied assmall drops on a surface.

A preferred embodiment of BAP printing is characterized in that thevertical extension of the colourants exceeds the vertical extension ofthe blank ink drops. Another preferred embodiment is characterized inthat the digitally applied blank ink drops penetrate downwards andupwards from the surface after application. A very wear resistant printmay be obtained with a printing method comprising blank ink and dry inkwith wear resistant particles preferably incorporated in the dry ink.

Several layers of prints may be position above each other and this maybe used to increase the wear resistance further and to create 3Ddecorative effects.

Static electricity or ultrasound may be used to apply and/or to removethe non-bonded powder particles. Airstreams and vacuum that blows awayand/or sucks up particles may preferably be combined with brushes. Ingeneral, all dry and wet methods that are used to remove dust may beused separately or in various combinations to remove the non-bondedparts of the dry ink. However, dry and non-contact methods arepreferred.

A controlled complete or partial removal of the non-bonded dry inkparticles is essential for a high quality print with a pre-defineddecorative image. Advanced removal systems may also be used that onlyremoves the colourants, for example, colour pigments while an essentialpart of the transparent melamine powder particles may remain on thesurface. This may be accomplished by, for example, a two-stepapplication where a first layer comprises only melamine resin orparticles that are applied to the surface prior to the application ofthe blank ink with the colourants. This first layer is preferablystabilized. It may be sprayed with water and dried by, for example, IRor hot air. This separate binder layer that preferably comprisesmelamine may in some applications replace, for example, pre-impregnatedpaper, that in some application may be used as a surface layer 2, andonly non-impregnated paper with or without a base colour may be used asa surface 2 for the print application cycle.

The moisture content of the surface layer should be accuratelycontrolled in order to facilitate the removal of the non-bonded powderparticles. Moisture content below 8% or even more preferably notexceeding 6% is preferred. The surface layer 2 may be dried by, forexample, IR lamps prior to the application of the blank ink. Specialchemical may be applied in order to seal the surface 2 or the upper partof the bonded colourants in order to create a sealing or a release layerthat may prevent colourants to stick to specific parts of the surfacelayer where no blank ink is applied.

The floor panel 1 comprises generally a lower balancing layer 4 oflaminate, plastic foils, coated paper or like material. Such balancinglayer may also be applied as a dry mix of melamine powder and woodfibres, which are stabilized by moisture and heat prior to pressing.Pigments may be included in the powder mix to provide a base colour. Thebalancing layer may also comprise only melamine powder or a liquidmelamine resin, which is applied directly on the rear side of the core3, and no paper or wood fibres are needed to balance the surface layer.The melamine content in the surface layer is preferably higher than inthe balancing layer. The rear side of the panel is very suitable toprovide specific information to the floor installer or end consumer.Conventional digital printing or BAP printing may be used to create adigital pattern or text on the balancing layer. Installation andmaintenance instructions, logos, other type of instruction, pictures andinformation may be included and may replace information that isgenerally applied on the packaging or in special separate instructions.The digital print and especially the BAP print may be very costefficient since only one digitally applied colour is generallysufficient in addition to a base colour. The backing layer may also havea digital print that is only decorative.

FIGS. 3a-3d show an embodiment of the invention, which is based on asecond principle where dry ink 15, comprising colourants 7 andpreferably also a binder that may be melamine 13, in a first step isapplied on a surface 2. A digital print is thereafter as a second stepformed by the digital drop application head that applies a blank inkpattern BP by means of the blank ink on the dry ink. A main differencebetween the first and the second principle is the sequence ofapplication of the blank ink and the dry ink. The blank ink 15 isaccording to the first principle applied in a first step while accordingto the second principle the blank ink 15 is applied in a second step.The first principle is below referred to as “Binder Under Powder” BUPprinting and the second principle is referred to as “Binder On Powder”BOP printing. The BUP and BOP digital print may be a direct print or atransfer print as described above.

These two principles BUP and BOP may provide different images withdifferent colour intensity. The blank ink drops 11 will when appliedaccording to the first BUP principle form ink spots when they hit thesurface and such ink spots will cover a much larger area than thediameter of the drops. Only a part of the liquid substance from the inkspots will penetrate from the surface and into the dry ink. When theblank ink drops are applied according to the second BOP principle, theywill first penetrate into the dry ink particles that will be bondedtogether in small particle clusters and a smaller part of the liquidblank ink drops will reach the surface 2 where the small clusters willbe bonded to the surface. Such application may be used to preventbleeding in some application where the surface has an open structurethat distributes a liquid substance. It should be mentioned thatbleeding is not always a disadvantage since it may be used to createdecorative effects. The application of dry ink must be accuratelycontrolled when the BOP principle is used and the maximum thickness ofthe dry ink layer should be adapted to the drop size and drop intensitysuch that the blank ink penetrates through the dry ink layer and to thesurface. The thickness of the dry ink layer should preferably not exceedthe maximum penetration level of the dry ink drops.

The thickness of the dry ink layer may vary considerably when the firstBUP principle is used since excess non-bonded particles above thepenetration level of the blank ink drops applied on the surface willautomatically be removed and liquid substance on the upper part of thedry ink particles may be dried. The thickness of the dry ink layer maybe larger or smaller than the penetration level of the blank ink dropswhen the BUP principle is used. This provides the possibility to usecombinations of blank ink drop intensity and vertical extension of thedry ink to create colour variations.

Both principles have advantages and disadvantages depending onapplication.

The blank ink 11 may even in this embodiment comprise water that whenapplied melts, for example, melamine particles 13 mixed with pigments 12or melamine particles applied under the pigments. The binder connectssome pigments that form the same patter as the binder pattern BP whileother non-bonded pigments are removed. FIG. 3a shows dry ink 15comprising a mix of melamine powder 13 and pigments 12 scattered on asurface 2. FIG. 3b shows a digitally applied blank ink pattern BPapplied on the dry ink. FIG. 3c shows that non-bonded pigments and inthis preferred embodiment also melamine particles 13 have been removed.FIG. 3d shows a BAP printing station 40 comprising a scattering station27 a blank ink application station 36, a IR oven 23 and a dry inkremoval station 28 based on an air stream and vacuum.

The first and the second principles may be combined. Blank ink 11 may beapplied prior and after the application of the dry ink 15 and this maybe used to bond a thicker layer of colourants and to create a solidprint with a large vertical extension and high wear resistance. Binderprinting equipment may comprise binder-printing stations that apply dryand blank ink according to the first and the second principle.

FIGS. 4a-4d show embodiments of the invention, which are based on athird principle where the bonding of the dry ink 15 is accomplished withdigitally controlled heat that activates a heat sensitive resin andbonds the dry ink 15 to a surface 2 such that a digital print P isformed when non-bonded dry ink particles are removed. Dry ink 15comprising colourants 7, preferably pigments 12, may in a first step beapplied on a surface 2 as shown in FIG. 4a . A binder pattern BP orimage is thereafter formed digitally by dry methods and non-bondedcolourants 7 are thereafter removed as shown in FIG. 4c . Severalmethods may be used. FIG. 4d shows a laser beam 29 that melts or cures abinder, for example a thermosetting or thermoplastic resin 13 that maybe mixed with the blank ink or included in the surface 2. The dry inkmay also be connected electrostatically to the surface by the laserbeam. A digitally created print P is obtained when the non-bonded ornon-connected colourants, are removed. The laser beam may be used tocreate a binder pattern with heat or electrostatically prior and/orafter the application of the colourants according to the first and thesecond principles described above for the application of the blank ink.

FIG. 4d shows a binder printing station 40 comprising a dry inkapplication station 27, a laser 29 and a dry ink removal station 28based on an air stream and vacuum. The laser 29 may be replaced withheating lamps that may be used to create images that comprise, forexample, rather large areas of the same colour as in some stone designsor base colours in wood grain designs.

FIG. 4d shows also that a heat bonding station 26 with heating printheads 80 comprising several small heating elements may be used to createhigh-resolution prints with dry bonding methods. The heating print head80 may apply direct heat that bonds dry ink 15 particles preferablycomprising pigments 12 and a heat sensitive resin. The heating printhead 80 may also apply indirect heat by heating a heat transfer foil 81that may be in contact with the heating print head 80 and the dry ink 15particles. The heat transfer foil 81 may be a copper or aluminium foiland may comprise individual small elements with high thermalconductivity, for example, elements made of copper or aluminium, thatare imbedded in a heat insulating carrier that prevents heat to spreadbetween individual elements. The heat transfer foil 81 may be used toincrease the printing capacity. A heat pulse from the heating print headwill heat a portion of the foil and the heat will be maintained when thefoil follows the surface and transfers the heat to the dry inkparticles.

Even a conventional laser system based on the above described impactmethod may be used to apply a digital print partly or completely on abuilding panel or in combination with the above described binderprinting methods.

All the above-described principles may be partly or completely combinedand a production line may comprise several digital binder printingstation according to the first, second or third principles.

FIGS. 5a-5h show schematically side views of application of twodifferent colours according to the first BUP principle. A first binderor a spot of blank ink 11 a, that in this embodiment comprisesessentially water, is applied by a thermal digital drop application inkhead on a surface 2 that may be a stabilized powder layer or a paper asshown in FIG. 5a . The jets 50 from the head apply drops of blank ink 11by the nozzles 54 when the heater 59 creates bubbles 60 in the inkchamber 52 such that the blank ink drops 11 form liquid spots 11 a whenthey hit the surface 2. The digital drop application head may also be aPiezo head and the water based blank ink may also comprise a viscosityincreasing substance. The water based blank ink may comprise glycol orglycerine.

A first dry ink layer comprising colour pigments 12 a and dry particlesof a binder, in this preferred embodiment melamine particles 13 a, isapplied on the surface 2 and on the liquid blank ink spots 11 a as shownin FIG. 5b . Melamine particles 13 a that are in contact with the wetwater based drops will melt. A first IR lamp 23 a may be used to dry thewet melamine and to bond the pigments to the surface as shown in FIG. 5cand the non-bonded melamine and pigment particles are thereafter removedsuch that a pigment image or décor 12 a that corresponds to the appliedbinder pattern formed by the blank ink drops 11 a is obtained as shownin FIG. 5d . FIGS. 5e-5h show that the same application may be repeatedwith a new application of dry ink comprising pigments 12 b havinganother colour and mixed with melamine particles 13 b and a new binderpattern 11 b such that a two colour image is obtained with two types ofcolourants or colour pigments 12 a, 12 b bonded to two patterns of blankink 11 a, 11 b as shown in FIG. 5 h.

FIG. 6a shows an embodiment where the digital BAP printing equipment 40comprises a digital blank ink application station 36, a dry inkapplication station 27, IR drying or curing 23 and a dry ink removalvacuum station 28. The BAP printing equipment 40 is in this preferredembodiment combined with a conventional ink jet printer 35. The BAPprinting method may be used in this combination to create the major partof a digital print while some parts of the final print may be created bya conventional ink jet printer. This may reduce the ink costconsiderably since, for example, the cost effective BAP method, where nopigments have to be handled by the digital drop application head, mayapply, for example, 90% of the pigments which are needed to create afully printed digital décor or pattern. Powder based floors areparticular suitable for this combined method. A first base colour may beprovided by the powder layer 2 a. A second coloured pattern may beapplied by the BAP printing equipment and a third colour may be appliedby conventional digital printing equipment. No stabilization of thesecond colour is needed since no additional dry colourants will beapplied and removed. This embodiment is characterized in that athree-colour image is formed by a base colour, preferably included inpowder or in a paper layer, dry colourants and liquid ink. The same typeof print heads may be used to apply the blank ink and the conventionalliquid ink.

A conventional digital printer may be used to apply blank ink that isused as binder for the dry ink and a conventional liquid ink comprisingcolourants. One or several ink channels may, for example, be filled withblank ink that has different drying and/or bonding properties than theother channels comprising conventional pigment based ink. The blank inkdrops may be wet when the pigment-based drops have dried. The blank inkmay be used to apply colourants that form the major parts of the colourof a digital print.

FIG. 6b shows a binder and powder printing equipment 40 where dry ink15, comprising, for example, a mix of pigments 12 and melamine powder 13is applied by a scattering station 27 comprising preferably an embossedroller 22 and preferably an oscillating brush 42. The non-bondedcolourants, for example, pigments and melamine particles are removed bya dry ink removal station 28 that recycles the mix 12, 13 or the blankink into the scattering station 27. A pigment/melamine dust cloud may becreated by airstreams and only the pigments and melamine powder thatcome into contact with the wet binder 11 will be bonded to the surface2.

FIG. 6c is a cross section of a floor panel 1 and shows that the BAPprinting method is especially suited to apply a digital BAP print on afloor panel with a paper based or powder based surface 2 and with amechanical locking system comprising a strip 6, with a locking element 8in one edge that cooperates with a locking groove 14 in an adjacent edgeof another panel for horizontal locking of the adjacent edges and atongue 10 in one edge that cooperated with a tongue groove 9 in anotheredge for vertical locking of the panels. Such floor panels havegenerally advanced embossed wood or stone decors that require largeamounts of different colour pigments and a decor that has to bepositioned accurately in relation to embossed structures and the paneledges where the mechanical locking system is formed. Generally the décormust be adapted to the edge part of the surface portion that is removedwhen the locking systems are formed. FIG. 6c shows a wood grain patternwith a first S1 and a second S2 surface portion having differentcolours. The second surface portion S2 that in this embodiment extendsmainly in the length direction L of the floor panel is applied on abasic layer 2 comprising the first surface portion S1.

FIG. 6d shows a dry ink removal station 28, that in this embodiment isbased on air streams and vacuum that blow away and sucks up particles.One or several vacuum-sucking profiles 41 with openings that cover thewhole width of the applied dry ink layer may be used to removeessentially all non-bonded dry ink particles 11. One or several airknifes 42 that also cover the whole width may applies an air pressure onthe remaining non-bonded particles such that they are released from thepanel surface 2 and blown into the vacuum—sucking profile. The majoradvantage with this combined method is that high air pressure is moreefficient and creates a stronger air stream than vacuum. This method maybe used to remove essentially all visible dry ink particles from roughsurfaces such as a stabilized powder surface and rough paper surfaces.Even very small particles, for example, small pigments or very smallwood fibres may be removed. A two-step process may be used to recycledry ink. A first removal is made with a dry ink removal station thatonly comprises a vacuum-sucking device and that removes all very looseparticles, which may be about 90% or more of the non-bonded dry inkparticles. Such particles are generally very clean and may be reused. Asecond combination dry ink removal station 28 based on vacuum and airpressure as shown in FIG. 6d may be used to remove the remainingparticles that may contain some particles from the powder based surface2 or from a precious application of another colour. Such particles maynot be suitable for a recycling.

All the above-described methods may be partly or completely combined.

FIGS. 7a-7c describes application and removal of colourants 64 havingdifferent sizes and how a solid print P may be formed by pressingtogether dry ink 11 particles.

Application and removal of colourants are, in some applications,important for a high quality image. In some other application it may bean advantage if some colourants are left on the surface since this maybe used to create a more realistic copy of, for example, wood designswhere the wood surface generally always comprises some small defects andcolour spots that are distributed in a random fashion. Small particlesare also difficult to see and will in many applications not disturb theoverall impression of the décor, especially if they are not applied in araster pattern.

FIG. 7a shows that very small particles with a size of 10-20 microns andsmaller may have a tendency to stick to a surface 2 that, for example,may be an uncoated paper surface comprising wood fibres 61 with a ratherrough fibre structure. FIG. 7a shows also a pressed part A and anunpressed part B of a panel surface 2. The blank ink drops are appliedin a raster pattern R1-R4. The unpressed part B show pigments 12 a thatafter the removal of the dry ink are bonded to the blank ink and otherpigments 12 b that are not bonded by the blank ink but that are stillattached to, for example, paper surface after removal due to friction orstatic electricity. The pressed part A shows pigments 12 c that arepermanently bonded to the surface 2 by pressure and heat. Pigments 12 cthat have been applied above each other are pressed to a flat and solidprint P with overlapping pigments. A BAP print provides the possibilityto create a print that corresponds to a practically indefiniteresolution by using a rather low resolution, for example 300 DPI, whenapplying the blank ink 11. Such a printed pattern may be practicallyidentical to a wood grain structure in real wood or a stone pattern in areal stone where patterns are formed by different natural fibres orcrystal structures.

FIG. 7b shows that the sticking problem may be solved with dry ink thatcomprises colourants 7 that are larger than, for example, conventionalpigments 12. The colourants are preferably in the range of 30-100microns. In some applications colourants with a size of up to 300microns or more may be used depending on the décor. Such comparativelylarge macro colourant particles 64 may be formed in many different ways.The macro colourants 64 comprises according to one preferred embodimentpigments 12 attached to a particle body 66. The particle body is in thispreferred embodiment a spray dried melamine particle 13. Such macrocolourant particles 64 with a size exceeding 20 microns are much easierto scatter and to remove than small pigments with a size of a fewmicrons or smaller. A advantage is that pigments are attached on severalparts of the particle body 66—on lower 66 a and upper parts 66 b—asshown in FIG. 7c , which is a side view of a macro colourant 64 shownfrom above in FIG. 7b . A spot 57 of a liquid blank ink 11 bonds a macrocolourant particle 64 comprising several pigments 12. The pigments 12are positioned vertically over each other on opposite sides of aparticle body 66 and such embodiment may provide a deeper print withincreased colour intensity and wear resistance. Another advantage isthat a small blank ink spot 57 may be used to bond a large amounts ofcolourants or pigments that in fact may have a mass or size that islarger than the mass or size of the blank ink spots applied as dropsfrom a digital drop application head 30′. A large amount of pigment orcolourants may be bonded in this way with rather small drops of blankink. For example one gram of blank ink may bond 1-5 grams of colourants.This is a major difference compared to conventional digital printingwhere the liquid ink generally only comprises 20% pigments and the inkdrop comprises always a smaller amount of colourants than the ink dropitself. Generally about 5 grams of conventional pigmented ink must beapplies in order to apply 1 gram of pigments on a surface.

FIGS. 8a-8h show preferred embodiments of macro colourant particles 64.Such particles may comprise or consist of several individual colourantparticles 69 that may be connected to each other to macro colourantparticles 64 having a specific colour. The macro colourant particles 64may also be produced by a combination of several materials and chemicalshaving a particle body 66 and pigments included in the particle body 66or attached to the surface of the particle body. FIG. 8a shows anembodiment comprising several individual colourants 69, for examplepigments 12, that are connected to each other with a binder and thatform a macro colourant particle 64. Such macro colourants may beproduced by mixing, for example, pigments 12 with a liquid thermosettingresin, for example melamine. The mix is dried, milled and sieved intomacro colourants comprising pigment clusters of a pre-determined size.

FIG. 8b shows a macro colourant particle 64 having a particle body 66 ofa spray dried thermosetting or thermoplastic resin, that comprisespigments 12 a, 12 b in the particle body 66 and on its surface. Thepigments may be of different colours. The colourant in the body 66 mayalso be a dye. Mixing, for example, a liquid thermosetting resin, forexample melamine, with pigments or dyes prior to the spray drying may beused to produce such particles. The pigment on the surface may also beattached by mixing pigments with the spray-dried particles. The pigmentswills stick to the surface of the spray dried particle body. The bondingstrength may be increased if the mixing is made under increased humidityor heat especially when the particle body comprises melamine. Themelamine-based particles may be heated in a final stage where thepigments will be firmly bonded to the body. The curing level of themelamine particles may be increased and this will prevent bleeding ofthe pigments during a final pressing and curing of the printed surface.The macro colourant particles 64 have preferably a diameter of about30-100 micron and pigment content may be 10-50% of the total weight. Theresin may be melamine or polyacrylate. A binder may also be added to themix in order to increase the bonding between the pigments and theparticle body.

FIG. 8c shows a macro colourant particle 64 comprising a thermosettingor thermoplastic particle body 66 with colour pigment 12 in the particlebody 66.

FIG. 8d shows that, for example, macro colourant particles 64 may bemineral particles that comprise natural colours. Sand or stone powder orvarious types of minerals derived from, for example, oxygen, silicon,aluminium, iron, magnesium, calcium, sodium, potassium and glass powdermay be used. A preferred material in some applications that intend tocopy stone is sand that is a naturally occurring granular materialcomposed of finely divided rock and mineral particles. The compositionand colour of sand is highly variable, depending on the local rocksources and conditions, but the most common types of sand comprisessilica (silicon dioxide, or SiO₂), usually in the form of quartz.

A preferred embodiment is aluminium oxide 63 that is very suitable tobond and coat with a melamine resin.

Mineral particles and especially coloured glass particles comprisingpigments, similar to the glazing powder used in tile production, arevery suitable for BAP printing on tiles but may also be used in otherBAP applications. A BAP print may be applied on a tile body comprising abasic glaze layer with a base colour. Such basic glaze layer may bepre-pressed or applied in wet form and dried. The BAP print may duringfiring of the tile melt into the basic glazing layer. A transparentglaze layer may also be applied over the BAP print. A binder may beapplied on the basic glaze layer, on the coloured glass particles or inthe dry ink such that an application bond may be obtained by exposingthe blank and dry ink to, for example, IR light or hot air.

FIG. 8e shows that essentially all minerals, such as, for example,aluminium oxide particles 63, may be coated with a thermoplastic orthermosetting resin, for example, melamine 13. The resin may be used tobond colour pigments 12 to the particle body 66. Such macro colourants64 are very easy to apply on and remove from a surface and they mayprovide a very wear resistant print with pigments applied on the upperparts and the lower parts of the particle body 66. A preferred averagesize of mineral based macro colourants is about 100 microns. Thisparticle size may be used to create a wear resistant print with aparticle depth of 100 microns. The binder content is preferably 10-30%and the pigment content is preferably 5-25% of the total weight of themacro colourant particle.

Mineral particles comprising an aluminium oxide particle body 66 coatedwith pigments and a melamine resin are especially suitable to be used asdry ink when a bonding is made with a heating print head 80. Aluminiumoxide particles have a high thermal conductivity and melamine resin maybe bonded with a heat of about 100 degrees C.

FIG. 8f shows that the macro colourant particles 64 may comprise naturalfibres—for example, wood fibres 61. No pigments are needed since thefibres may have natural colours. Fibres from a lot of different woodspecies may be used, for example, from softwood such as pine and spruceand hardwood such as ash, beech, birch and oak. The colours may bemodified by heat treatment. Even cork particles may be used. Suchnatural colourants may be coated with a binder, preferably athermoplastic or thermosetting resin, for example melamine. The coatingmay be used to improve scattering properties and/or as a binder to bondthe macro colourant to the surface and the binder pattern created by theblank ink.

FIGS. 8g and 8h show macro colourant particles 64 comprising wood fibres61 and wood chips 62 that have been coated with a resin and pigments 12.

Fibre based macro colourants may be used to create an almost identicalcopy of wood. Wood fibres having different colours form the wood grainpattern in a real wood plank. The BAP printing method allows that thesame principles may be used with different fibres that actually form thewood grain pattern and not small ink drops arranged in a raster pattern.This is shown in FIG. 6c . The panel 1 has a surface with a wood graindecor comprising a first surface portion S1 that is formed by a basiclayer 2 comprising wood fibres 61 a having a first colour. A secondsurface portion S2 is formed by wood fibres 61 b having a second colour.The wood fibres having the second colour are applied on and bonded tothe basic layer. The basic layer is preferably continuous. The secondsurface portion S2 covers preferably a part of the first surface portionS1. The base layer 2 may be a powder mixed with a thermosetting resin, acoloured paper or a coloured wood based core. The fibres in the twosurface portions S1, S2 have preferably different average sizes. Thefibres in the second surface portion S2 are preferably smaller than thefibres in the first surface portion S1. The second surface portions S2comprise preferably a pattern with a length L that exceeds the width W.

The coating with resins may be used to bond pigments to the particlebody and to bond the macro colourant particle by the blank ink to thesurface. The coating may be made in several steps with intermediatedrying and curing of the resin. It is preferred that a first coating,drying and curing with a thermosetting resin, for example, a melamineresin is made under higher temperature than the second curing. The firstcuring may be made such that the melamine resin is cured to anessentially C stage where the melamine will not float during the finalpressing operation and this will eliminate bleeding of the pigments. Thesecond coating is preferably cured to a B stage where the melamine ispossible to melt with the dry ink. Dry ink particles may be producedfrom wood fibres 61 that are mixed with pigments and melamine resin andthey are thereafter pressed under increased temperature such that themelamine resin cures. The pressed mix may be milled into small particlesand coated with liquid melamine resin and dried such that the outermelamine coating is in a B stage. A binder layer may be applied betweenthe pigments and the particle body and on the pigments such that theyare completely coated with a binder layer. Several layers of pigmentswith different colours may be bonded to a particle body of a macrocolourant.

Dry ink may comprise a mix of several different types of macro colourantparticles, for example, melamine/minerals, melamine/fibres,fibres/minerals etc. and the structure and the size of the macrocolourants may be used to create special décors.

The coating of the particle body 66 is preferably made in several stepswhere, for example, particles such a fibres or minerals in a first stepare mixed with a resin, preferably spray dried melamine, and pigments.This mix may be applied as a rather thin layer, with a thickness of, forexample, 1-3 mm, on a conveyor. The mix is as a third step sprayed withwater and dried by hot air or an IR lamp. The particle body, in thisembodiment the fibres or minerals, are coated and impregnated with thewet melamine and the pigments are bonded to the particle body. The smalllayer thickness makes it possible to dry the layer during a short dryingtime, for example a minute, and the resin may still be in a semi-curedB-stage. The dry mix is removed from the conveyor by, for example,scraping and the dry flakes are milled and sieved to pre-definedparticle sizes. The spray dried melamine particles and water may bereplaced with a wet binder, for example wet melamine that may be sprayedon a mix comprising pigments and particles that forms the particle body66.

The pigments may also be bonded to the particle body 66 with a binderthat comprises water based acrylic emulsions.

Macro colourants may provide a print that is very similar to an originalwood or stone design especially when fibres are used to copy a woodgrain pattern and minerals are used to copy a stone design. Conventionalrotogravure methods with a printing cylinder may be used to apply blankink on a surface. Dry ink comprising macro colourant particles may beapplied on the blank ink and non-bonded particles may be removedaccording to the BAP printing principles described above. Such printingmethod may be used to provide an advanced print comprising a design thatis not possible to create with conventional ink.

Macro colourants may be used to create a pattern, preferably a wood orstone pattern in LVT floors. The BAP printing method may be used toapply a print on the core, on the foil or on the lower or upper side ofthe transparent protective layer. Colourants may be melted into thelayers during the pressing operation. Prints in different layers locatedvertically above each other may create a 3D effect. Printing ontransparent layer may create an even more realistic 3D effect.

FIGS. 9a-9e show BAP printing with dry ink comprising macro colourants64 with a fibre based 61 particle body 66 coated with a melamine resin13 and pigments 12. Jets 50 from a preferably thermal ink head applydrops of blank ink 11 in a raster pattern R1-R4 that form blank inkspots 57 on a surface 2 that in this embodiment is a pre-pressed powderlayer applied on a core 3 as shown in FIG. 9 a.

FIG. 9b shows a dry ink layer 15 comprising fibre based macro colourants64 applied on the surface 2 and FIG. 9c shows the dry ink layer whennon-bonded macro colourant particles have been removed. The blank ink 11penetrates into the dry ink layer 15 from the surface and upwards due tocapillarity and the binder properties and several macro colourantslocated vertically above each other may be bonded by blank ink spots 57.The horizontal extension H2 of individual colourants, preferably macrocolourant particles 64, exceeds preferably the horizontal extension H1of the ink spots 57 and the vertical extension V2 of the dry ink layer,after the removal of the non-bonded particles, exceeds preferably thevertical extension V1 of blank ink spots 57. The vertical extension V1of the blank ink spots is generally about 10 microns or smaller. Thevertical extension V2 of the applied and bonded blank ink layer, afterthe removal of the non-bonded particles, may be at least 50 microns oreven larger, preferably larger than 100 microns. This is a majordifference compared to traditional ink jet printing where pigments areincluded in the ink drops. BAP printing allows that a print comprisinglarger volumes of colourants may be formed than the volume of the blankink applied by the digital drop application head.

FIG. 9d shows the BAP print P after a stabilization step that in thisembodiment is a pre-pressing operation. The macro colourants 64 may bepartly pressed into the powder-based surface 2.

FIG. 9e shows the powder-based surface in a completely cured stage afterthe final pressing operation. The macro colourants 64 are pressed intothe powder based surface 2.

The print P comprises pigments 12 a, which are located in a firsthorizontal plane Hp1 at the upper part of the surface 2 a and pigments12 b located at a second horizontal plane Hp2 below the particle body 66and below the first horizontal plane Hp1. The macro colourants 64comprise pigments 12 a, 12 b on the upper and lower side of the particlebody 66.

The macro colourant particles are applied at random and are preferablyoffset in relation to the raster pattern R1-R4 where each row and columnrepresent one pixel and one dry ink spot 57. The print P may be a solidprint with several macro colourants connected to each other and/oroverlapping each other. The BAP print in this preferred embodiment ischaracterized in that the blank ink 11 is applied in a raster pattern(R1-R4) and that the dry ink 15 is applied at random with overlappingcolourants 7 or macro colourants 64. Preferably the size of a macrocolourant particle 64 is such that it covers several pixels in a rasterpattern.

The thickness (diameter) of the fibres 61 is preferably about 10-50microns and the length may be 50-150 microns. The length may in someapplications also exceed 150 microns and realistic wood grain designsmay be formed with fibres having a length of about 100-300 microns.

FIG. 10a-10c show a BAP print with a very high wear resistance. Macrocolourants 64 a comprising a particle body 66 of aluminium oxideparticles 63 coated with pigments 12 a and a melamine resin 13, areapplied on a surface, that in this embodiment is a powder based surface2 a comprising melamine powder and pigments and preferably also woodfibres. The surface includes preferably a base colour. A layercomprising macro colourants that gives the panel a basic colour may alsoform the surface 2 a and may be applied directly on a wood or plasticbased core, a tile body or on a surface comprising powder, paper a foiland similar surfaces. FIG. 10a shows macro colourants 64 a bonded to thesurface 2 a by blank ink 11. FIG. 10b shows a second layer of macrocolourants 64 b comprising pigments 12 b with a different colour. FIG.10c shows the final cured surface with macro colourants that are pressedinto the powder based surface 2 a and preferably covered with atransparent layer, preferably a melamine layer 2 b that may be appliedafter a pre-pressing operation but prior to the final pressing step. Thetransparent melamine layer 2 b may also comprise bleached transparentwood fibres. It may be an overlay, a lacquer, a foil or a glazing. Ahigh wear resistance may be reached since a considerable part of thesurface 2 a, 2 b, including the particle body 66 of aluminium oxideparticles 63, must be worn of before all pigments 12 a, 12 b in theprint P are removed. Aluminium oxide particles with or without pigments(not shown) are preferably also included in the powder base surfacelayer 2 a and/or in the transparent melamine layer 2 b. The method mayalso be used to apply a wear resistant digital print on many othersurfaces such as paper, foils, tiles and other surface layers describedin this disclosure.

FIG. 11a shows a BAP equipment comprising several BAP printing stations40 a, 40 b that each is used for a print forming cycle that applies onespecific colour. Each BAP station comprises a digital drop applicationhead 30′a, 30′b and a combined dry ink application and removal station27 a, 28 a 27 b, 28 b and pre-pressing units 37 a, 37 b that stabilizethe dry ink 15 such that a new dry ink layer may be applied and removedaccording to the principles describe above. An embodiment of unit mayreplace an IR lamp. An embodiment of unit 37 a comprises preferably aheating 38 c and a cooling 38 d roller, a belt 20, and a pre-pressingtable 39. These parts may in some applications be replaced by just oneroller. A liquid release agent 19 may be applied on the belt 20 byrollers 38 a, 38 b or brushes or similar devices. Preferably the dropapplications heads 30 a′, 30 b′ use the same blank ink 11 to provide aprint P with several colours. This is an advantage compared toconventional printing. The BAP printing method allows in fact that thefinal printing ink is mixed and produced in line when the blank ink 11and the colourants 7 from the dry ink 15 are attached to each other onthe surface 2.

FIG. 11b shows schematically a compact BAP printing station 40 where,for example, one set of digital drop application heads 30′ aligned inone row, each comprising one ink channel, and one set of IR lamps 23 orpre-pressing units may be combined with several dry ink 15 applicationstations 27 a, 27 b, 27 c positioned in the feeding direction after thedrop application head 30′. One row of drop application heads 30′ mayapply colourants with many different colours. The blank ink, thatpreferably is an essentially transparent liquid substance, comprisespreferably a different colour than a first and preferably also a seconddigital pattern formed by the drop application head 30′. This is a majordifference compared to conventional digital printing where each printhead applies a specific colour and this colour is always the same as theliquid substance applied by the print head. A surface layer 2 or asurface that is a part of a floor panel 1 may be displaced in twodirections and each cycle may be used to apply one specific colour withthe same drop application head. The BAP printing station may comprise IRlamps or pre-pressing units and dry ink application stations on bothsides of the digital drop application head and different colours may beapplied when the surface 2 is displaced under the head 30′ in eachdirection. This means, for example, that three colours may be applied bythe same drop application head 30′ on a base colour when a panel 1 isdisplaced under the head 30′, back again to its initial position andunder the head again. The speed may vary between the various applicationsteps. This may be used to increase the capacity. A wood grain patternis generally made up of different amounts of specific colourants. Thespeed may be increased when the amount of a specific colourant is lowsince only a small amount of blank ink has to be applied on the surface.A digital control system may be used to optimize the capacity and toadapt the speed to the amount of blank ink 11 that is needed to form aspecific digital pattern. Several alternatives may be used to combineone blank ink drop application head with several dry ink applicationsstations and removal stations. A panel may after the first print formingcycle be displaced vertically or sideways to a conveyor that brings itinto an initial position. An intermediate stacking unit may also beused. Paper and foil material in rolls may be printed several times withthe same drop application head and the same blank ink.

FIG. 11c shows a pre-pressing unit 37 that may be used to pre-press apowder layer with a basic colour prior to the BAP printing. Such apre-pressing unit may also be used to stabilize the prints or topre-press and connect a powder based backing layer 4 on rear side of acore 3. When melamine is used as binder, a heating roller 38 c and apre-pressing table 39 may apply a heat of, for example, 90-120° C. and acooling roller 38 d may cool down the semi-cured layer 2 to atemperature preferably below 80° C. The pressing may be made at ratherlow pressures, for example, 5 bars or lower and the pressing time may beabout 10 seconds or shorter. The melamine will be pre-pressed to asemi-cured B-stage that may be further pressed and cured in a finalpressing operation. A sheet material with a pre-pressed powder basesurface and backing layer may be produced and used as a pre-finishedpanel. Other binders, for example, thermoplastic binders may bepre-pressed with other temperatures specifically adapted to the binderproperties.

FIG. 12a shows that a BAP printing station 40 and a pre-pressing unit 37may be combined into a BAP transfer printing station 41 and used incombination to create a digital BAP transfer print P on a surface 2.Blank ink 11 and dry ink comprising colourants 7, preferably pigments12, are applied on a transfer surface 18 that may be, for example, asteal or plastic belt or similar. The print P is pressed on a surface 2by rollers 38 c, 38 d and preferably by a pre-pressing table 38. The BAPtransfer printing unit may comprise a cleaning device 71, rollers 38 a,38 b or brushes that apply a release agent 19 and preferably also a IRlamp 23 that dries the release agent prior to the application of theblank ink 11. The release agent may also be mixed into the dry ink 15.

The BAP transfer printing method provides the advantages that blank anddry ink may be applied on a pre-defined transfer surface 18 that may bespecially adapted for an high definition application of blank inkwithout any risks for bleeding and an easy application and removal ofdry ink. This allows, for example, that a BAP print may easily beapplied on rather rough surfaces such as, for example, textiles,carpets, various board materials and similar surfaces. The BAP transferprint may be combined with all other described methods, for example, themethod described in FIG. 11b where one drop application head 30′ is usedto apply several colours.

FIG. 12b shows a BAP transfer printing station 41 where the belt hasbeen replaced by a roller 38 comprising a transfer surface 18. Theroller comprises preferably heating 25 a and cooling 25 b zones. Thenon-bonded dry ink may be removed by gravity that may be combined withultrasound, vibrations or air streams. This method may also be used toapply a direct BAP print on a flexible surface 2 a that may be a paper,a foil or similar. The application may be made in line with a pressingoperation or as a separate production step.

FIG. 12c shows a preferred embodiment of a floor panel 1 according tothe invention. The panel 1 comprises a backing layer 4 on the rear sideof the core 3 and a surface 2 on the upper part of the core comprising asub layer 2 c, a paper or foil 2 b and a wear layer 2 a over the paper.The backing layer 4 and the sub layer 2 c may be applied as dry melamineformaldehyde powder and the wear layer may be applied as a dry melamineformaldehyde powder comprising aluminium oxide particles. The paper maycomprise a base colour. A BAP print or a conventional digital print maybe applied on the paper. Such a dry process may be used to form a verycost efficient panel without any impregnation of a decorative paper or aprotective overlay. The spray dried melamine particles will melt duringpressing and impregnate the paper. It is obvious that this dry methodmay be used to save costs even when a conventional decorative paper isused.

FIG. 12d shows a method to form a base layer on rough core materials 3comprising cavities, cracks, splints or defects 3 a, 3 b. Such corematerial may be made of, for example, plywood or OSB. The problem isthat a powder layer generally has the same thickness at the cavities andat the upper parts of the core surface and there will not be sufficientamount of powder to form a high quality surface after pressing since thedensity of the surface layer will be lower at surface portions withcavities. This problem may be solved with a first powder layer 2 a thatis applied as filler and pressed by, for example, a roller or a rulerinto the cavities such that an essentially flat powder based surfacelayer 2 a is formed. A second powder based layer 2 b may be applied onthe first filler layer 2 a. The two layers may be pre-pressed asdescribed above and a base layer may be formed that in a second step mayprinted with a preferably BAP print and thereafter cured by heat andpressure.

The method may also be used without a print and only powder layerscomprising fibres, binders and preferably pigments may be used. Thisembodiment is characterized in that the powder content above cavities ishigher than the powder content above the upper parts of the core. Thepowder content may be measured by measuring the weight of the powderabove a cavity and above an upper part of the surface. The base layercomprising a first filler layer 2 a and as second powder layer 2 b maybe covered by a conventional decorative paper and also preferably with aprotective layer, for example a conventional overlay or a transparentlacquer.

FIG. 13a shows that a conventional laser printing technology that useselectrical charges to attract and release dry ink particles may beadapted such that digital prints may be provided on a core material 3comprising a surface 2 that preferably has a base colour. Negativecharged dry ink particles 15 that may be conventional laser tonerpigments, are applied by a developer roller 72 on a photo conductor drum70, which is in contact with a charge roller 71. A laser beam 29projects an image on the electrically charged photo conductor drum 70and discharges the areas that are negatively charged and anelectrostatic image is created. Dry ink particles are electrostaticallypicked up by the drum's discharged areas. The drum prints the print P onthe surface 2 by direct contact. An electrical charge may be applied tothe surface or the core such that the pigments are released from thedrum and applied on the surface. A fuse roller 73 fuses the dry inkparticles to the surface and bonds the dry ink particles. Aroller-cleaning device 74 may be used to clean the photo conductor drum.The dry ink particles may comprise a thermoplastic or a thermosettingresin that may be used to bond the particles to the surface with heatand pressure.

FIG. 13b shows that the laser printing technology may be used to apply atransfer print P on a surface 2. The dry ink particles are applied on abelt 20 comprising a transfer surface 18 and released from the photoconductor drum 70 by an electrical application roller 75 that applies anelectrical charge on the belt 20. The dry ink particles are then fusedby a pre-pressing table 39 that applies heat and pressure on the belt 20and the transfer surface 15. Heating 38 c and cooling 38 d rollers maybe used. The belt may be replaced by a transfer roller as shown in FIG.12 b.

FIG. 13c shows schematically several other preferred principles that maybe used to apply particles in well define patterns on a surface 2without a digital drop application head that applies a liquid binder ofblank ink.

A first principle is a method to create a base layer comprising at leasttwo different colours. A first layer 2 a with a first base colour isprovided as powder or as a coloured paper. A second colour of dry ink 15is scattered on the first basic colour. Some parts of the dry ink 15particles are removed with a dry ink removal station 28 comprisingseveral air nozzles 77 a, 77 b that may remove dry ink particles by, forexample, vacuum before they reach the surface with the base colour 2 a.The air nozzles 77 a, 77 b may be controlled digitally with preferablyseveral valves and a dry ink pattern P may be formed. This may berepeated and several colour patterns may be formed without any digitaldrop application heads or blank ink. This method is particular suitableto form patterns that partly or completely may be used to copy wood orstone designs. This method may be combined with digital BAP printing orconventional digital printing. The method may also be used to createdigital prints with high resolution. The dry ink 15 may compriseparticles with high density, such as minerals, especially aluminiumoxide particles or glass particles, that during scattering may fall in apre-determined essentially straight direction towards the surface 2 anda precise partial removal may be made with vacuum when the pass the airnozzles 77 a, 77 b. The applied dry ink is preferably stabilized bywater spraying prior or after the application.

The dry ink particles may according to a second principle pass through aset of electrodes, which impart a charge onto some particles. Thecharged particles may then pass a deflection plate 79, which uses anelectrostatic field to select particles that are to be applied on thesurface, and particles to be collected and returned for re-use by thedry ink application system.

According to a third principle a heating print head 80 that comprisessmall heating elements that produce varying amounts of heat similar tothe print heads used in the dye-sublimation or thermal printingtechnologies, may be used to attach colourants to a surface. Severalheating print heads 80 may be attached side by side such that they coverthe whole width of a printed surface. Rather low temperatures of about100 degrees C. may be used to obtain an application bonding of the dryink particles. The heat may also be rather high, for example 200-250° C.and such heat will not destroy wood fibres in paper and powder basedlayers. Several methods may be used to form a digital print with dry inkwhere the dry ink particles are bonded to a surface in a pre-determineddigitally print. Contrary to known technology such heating heads,combined with dry ink, may be used to apply a wide range of differentcolours without any heat sensitive papers or transfer foils. A thermosensitive binder, that may be a thermosetting or thermoplastic resin,wax and similar materials with a low melting points, may be included inthe surface layer or in the colourants of the dry ink. Powder comprisingdye-sublimation particles of different colours may be used as dry ink.The heating print head 80 may apply digitally controlled heat directlyon well-defined portions of the dry ink after application, or on thesurface layer prior to the application of dry ink. The heating ink headmay comprise heating elements arranged on an essentially flat surface oron a cylinder that rotates when a surface with dry ink is displacedunder the heating print head. Alternatively a heat transfer foil 81 asshown in FIG. 4d , may be applied between the dry ink and the heatingprint head 80 and may slide against the heating elements and the ceramicsubstrate of the heating print head. The non-bonded colourants ornon-vaporized dyes may be removed and reused.

FIG. 12a shows that a heating print head 80 may be used to provide heaton a transfer surface 18 that heats up the dry ink 15. The transfersurface may be used as a heat transfer foil 81. The heating print head80 may be located such that it provides a heat through a transfersurface 18 or on the dry ink 15 applied on the transfer surface 18. Theheating print head 80 may also heat up portions of a surface prior tothe application of dry ink. The surface may be a board material, powder,paper, a foil, a base coating, a transfer surface, and all other surfacematerials described in this disclosure.

FIG. 13d shows that heating print heads 80 and dry ink 15 are especiallysuited to be used to form a digital print P on flexible thin surfaces 2that preferably may be a paper, a foil, a textile material, and similarmaterials that generally have sufficient heat transfer abilities andheat resistance to function as a heat transfer foil 81. A powder andheat printing equipment may comprise a scattering station 27 thatapplies blank ink 12 on a surface, a heating print head 80 that bonds apart of the blank ink 15 with heat to the surface 2 and a dry inkremoval station 28 that removes non-bonded dry ink 15. In someapplication a pre-pressing unit 37, vacuum applied on the lower side ofthe surface or oscillation may be used to increase the contact betweenthe dry ink particles and the surface during the heat bonding. Aseparate heat transfer foil as shown in FIG. 4d may be used to increasethe printing capacity. The pre-pressing unit 37 may also compriseheating print heads and heat may be applied from the upper and/or thelower side.

The heating print head 80, with or without a heat transfer foil 81 mayreplace all digital drop application heads 30′ in the embodiments ofthis disclosure.

Embodiments of the three principles described above are based on themain method that colourants are applied as powder in dry form on asurface and bonded in a pre-determined pattern that forms a print. Thesurface may be a transfer surface 18 and the three principles may beused to provide a transfer print.

FIGS. 14a-14d shows a method to form a digital embossing on a surface 2preferably an EIR structure, hereafter referred to as BAP embossing. Adigital drop application head applies a pattern of blank ink on acarrier 68 as shown in FIG. 14a . Press particles 67 which are similarto the colourants shown in FIGS. 8d-8h may be applied on the carrier 68that may be an aluminium foil, plastic foil, paper and similar. Theapplication may be the same as for the BAP printing and all methodsdescribed above may be used to apply press particles 67 in a pattern ona carrier 68. However, the press particles 67 do not have to be coatedwith pigments. They may be coated with a thermosetting 13 orthermoplastic resin. In some application the blank ink is sufficient toprovide an application bond. A heating print head may also be used tobond the press particles 67 to the carrier. The carrier 68 and/or theblank ink may also comprise a binder. The particles are preferably hardminerals such as aluminium oxide, sand, stone powder and similar. Suchparticles that essentially maintain the original shape during pressingand are not compressed during a pressing operation are referred to ashard press particles. The size of the particles should be adapted to thedepth of the embossing. Particles with a diameter of about 0.2 mm may,for example, be used to create an embossing with a depth of at least 0.2mm. The carrier 68 with the press particles 67 is positioned andcoordinated with a printed pattern P that may be a conventional print ora BAP print applied on, for example, a powder or paper surface 2. FIG.14b shows the pressing step where the press particles 67 and the carrier68 are pressed by the press table 24 into the surface 2. FIG. 14c showsthe embossed structure 17 when the carrier 68 with the press particles67 is removed after pressing and a perfect digitally formed EIR surfaceis obtained that may be coordinated with any type of digital prints Pwithout any conventional press plates. A part of the surface structure,especially the microstructure 16 that provides the gloss level, may beformed by the carrier. The deep embossed structures 17 are formed by thepress particles and the carrier 68.

The BAP embossing provides the advantages that a deep embossing may beformed with only one or a few BAP application steps since considerableamount of press particles 68 may be applied with thin layers of blankink 11. This method allows that the embossing depth D exceeds thevertical extension V of the blank ink spots 57 that connect the pressparticles to the carrier.

FIG. 14d shows a method to form the surface 2 of a panel with BAPembossing. A blank ink application station 36 applied blank ink 11 on acarrier 68 that in this embodiment preferably is aluminium foil or acoated release paper. A dry ink application station 27 is used to applypress particles 67 on the carrier. An IR lamp 23 may be used in someapplications to create an application bonding. The press particles areremoved by a dry ink removal station 28 and the carrier with the pressparticles is pressed against the substrate by a press table 24. Thecarrier and the press particles are thereafter removed and a BAPembossed structure is formed.

The method may be used to form a conventional embossing or an EIRembossing.

The carrier 68 surface that is pressed against the embossed surface 2may be coated such that different gloss levels or microstructures may beobtained. Such coating is preferably made digitally according to amethod described in this disclosure.

The press particles 67 may be bonded to the carrier with all methodsdescribed above. For example heating print heads 80 and laser 29 may beused.

FIGS. 15a-15d shows that the BAP transfer print method may be combinedwith the BAP embossing method. Press particles 67 may be applied on oneside of a carrier 68 and a BAP print may be applied on the opposite sideof the carrier 68 that comprises a transfer surface 18 as shown in FIG.15a . The carrier 68 may be a foil, paper, and similar as describedabove. The BAP print may also be replaced with a conventional digitalprint or even with a print provided with conventional rollers.Preferably the print P and the pattern of the press particles 67 arecoordinated such that an EIR structure may be formed. FIG. 15b showsthat the carrier 68 and the press particles 67 together with the print Pare pressed on a surface 2. FIG. 15c shows that the print P is bonded tothe surface 2 and that the carrier 68 with the press particles 67 formsan embossed structure 17 when removed after the pressing operation. Theapplication of the press particles 67 and the dry ink print may be madein line with the pressing operation as shown in FIG. 15d or as aseparate operation where a pre-printed and pre-embossed carrier 68 isformed that may be supplied as an individual carrier preferably as afoil. A combined BAP printing and embossing equipment may comprise blankink application stations 36, dry ink application stations 27 and dry inkremoval stations 28 that apply and remove dry ink 15 and press particles67 on opposite sides of a carrier 68.

The particles may also be bonded to the carrier with a laser beam,heating print heads and all other methods described above.

The surface of the carrier 68 that is in contact with the panel surface2 may be pre-pressed and different gloss levels or microstructures maybe formed. Such pre-pressing may be made with conventional embossedcylinders or with a BAP embossing method. Various gloss levels andmicrostructures may also be formed with digital printing and a coatingmay be made according to any of the methods described in thisdisclosure. The carrier 68 with the press particles 67 and preferablyalso with a transfer print P may be supplied as a press matrix 78 andmay be used to form an embossed structure on, for example, laminate,wood and powder based floors but also on tiles and LVT floors. The pressmatrix 78 may be used several times. The print P may be a conventionalprint, a digital ink jet print, a digital BAP print or similar.

The method may also be used to form a more durable “mirror shaped” pressmatrix that may be a sheet material where protrusions on the carrier 68forms cavities in the sheet shaped press matrix. The carrier with thepress particles may be pressed against impregnated paper, preferablyphenol impregnated craft paper or powder comprising a thermosettingresin, and a structured sheet matrix may be formed that in a second stepmay be used as a press matrix. Metal powder and glass fibres may beincluded in order to improve the strength and the heat transferproperties.

All the above described methods may be partly or completely combined inorder to partly or completely create a digital print or and/or a digitalembossing.

Water based blank ink may in some application be combined or replaced byoil or solvent based ink. The advantage with oil-based ink may be thatit has a very long drying time and this may improve the function of thedigital drop application head.

Example 1 Dry Fibre Based Ink

Dry ink powder was produced by mixing 20% (weight) spray dried melamineformaldehyde particles, 20% dark brown colour pigments and 60% woodfibres of pine with an average length of about 0.2 mm and a thickens ofabut 0.05 mm. The mix was applied as 1 mm thick layer by scatteringequipment on a steal belt. The powder mix was thereafter heated andmoisture was applied by steam from deionized water. The mix was dried byhot air such that a hard stabilized powder based surface layer wasobtained with a semi cured melamine binder. The dried layer was removedfrom the belt by scraping and the dry wood particles coated withpigments and melamine resins were milled and sieved into dry inkcolourants with a size similar to the size of the individual woodfibres. A dry ink comprising colourants with a wood fibre body and witha surface covered by pigments bonded to the fibres by the semi curedmelamine resin was obtained.

Example 2 Digital Print with Heating Print Head

A 8 mm HDF board was sprayed with small water drops of deionized waterand a powder mix of 300 g/m2 comprising wood fibres, melamine particles,light brown colour pigments and aluminium oxide particles was applied byscattering equipment on the HDF core. The mix was sprayed again withdeionized water comprising a release agent and dried by IR light suchthat a hard stabilized partly semi cured powder based surface bonded tothe HDF core and with a light brown basic colour was obtained. The panelwith the stabilized powder surface was put on a conveyer and displacedunder digital Kyocera Piezo print head. Dry ink as described in example1 above, comprising a darker brown colour than the basic light brownpowder based surface, was in a second step scattered over the wholepowder based surface with a dry ink application station comprising ahopper and a rotating and oscillating engraved roller with a diameter of5 cm. A dry ink layer of about 30 gr/m2 was applied on the panelsurface. An aluminium foil was applied on the dry ink layer and thepanel with the aluminium foil was displaced under a heating print headthat formed a wood grain pattern. The aluminium foil was removed and thepanel was thereafter displaced with a conveyor under a dry ink removalstation comprising a vacuum-sucking profile with an opening that coveredthe whole width of the applied dry ink layer where essentially allnon-bonded fibers with the pigments were removed and an air knife thatapplied an air pressure on the remaining non bonded particles that werereleased from the panel surface and blown into the vacuum—suckingprofile such that essentially all visible dry ink particle were removed.A wood grain patter comprising a light brown base colour and a darkbrown wood grains structure was obtained. A protective layer comprisingdry a mix of dry melamine and aluminium oxide particles was scatteredover the entire surface with the same type of scattering station asdescribed above for the blank ink. The protective layer was sprayed withsmall water drops comprising a release agent and dried under IR lamps.The panel with the print and the protective layer was thereafterpositioned in a pre-determined position in relation to a long and shortedge in a hydraulic press and pressed against an embossed steel plateduring 20 seconds under a temperature of 170 C.° and 40 bars pressureand the powder-based surface with the wood grain pattern and theprotective layer was cured to a hard wear resistant surface with a highquality digital print coordinated with the embossed surface structure.The décor of the panel was created by a basic colour and a wood graindesign comprising wood fibres and pigments. The obtained copy of a wooddesign was very realistic since natural wood fibres were used to createthe visible pattern.

EMBODIMENTS

1. A method of forming a digital print (P) on a surface (2) wherein themethod comprises the steps of:

-   -   applying colourants (7) on the surface (2);    -   bonding a part of the colourants to the surface (2) with a        binder (11); and    -   removing non-bonded colourants (7) from the surface (2) such        that a digital print (P) is formed by the bonded colourants (7).

2. The method as in embodiment 1, wherein the colourants (7) comprisepigments (12) mixed with the binder (11).

3. The method as in embodiments 1 or 2, wherein the binder (11)comprises a thermosetting resin.

4. The method as in any one of the preceding embodiments, wherein thebinder (11) comprises a thermoplastic resin.

5. The method as in any one of the preceding embodiments, wherein thebinder (11) is a powder.

6. The method as in any one of the preceding embodiments, wherein thesurface (2) is a paper layer or a foil.

7. The method as in any one of the preceding embodiments, wherein thesurface (2) comprises a powder layer.

8. The method as in any one of the preceding embodiments, wherein thesurface (2) is a part of a building panel (1).

9. The method as in any one of the preceding embodiments, wherein thesurface (2) is a part of a floor panel (1).

10. The method as in any one of the preceding embodiments, wherein thecolourants (7) are removed by an airstream.

11. The method as in any one of the preceding embodiments, wherein thebinder is a blank ink (11) comprising a liquid substance that is appliedby a digital drop application head (30′).

12. The method as in any one of the preceding embodiments 1-10, whereina laser beam (29) or a heating print head (80) makes the bonding.

13. The method as in embodiment 11, wherein the liquid substance iswater based.

14. The method as in embodiments 11 or 13, wherein the liquid substanceis exposed to IR light (23) or hot air.

15. The method as in embodiment 14, wherein the liquid substance (11) isexposed to UV light.

16. The method as in embodiment 14, wherein the liquid substance isapplied with a Piezo ink head.

17. The method as in embodiment 14, wherein the liquid substance isapplied with a thermo ink head.

18. The method as in embodiment s 16 or 17, wherein the liquid substanceis applied with drops (56) arranged in a raster (R1-R4) and wherein thecolourants (7) are bonded with several drops.

19. The method as in any one of the preceding embodiments, wherein thecolourants (7) have a particle body (66) comprising fibres (61) ormineral material (63).

20. The method as in any one of the preceding embodiments, wherein thesurface (2) with the bonded colourants (7) is pressed.

21. The method as in any one of the preceding embodiments, wherein thesurface (2) with the bonded colourants (7) is heated and pressed.

22. The method as in any one of the preceding embodiments, wherein thesurface (2) comprises another colour than the colourants (7).

23. The method as in any one of the preceding embodiments, wherein themethod comprises additional steps of applying new colourants (7, 12 b)with a different colour on the first bonded colourants (7, 12 a) and onthe surface (2), bonding a part of the new colourants (7, 12 b) to thesurface with a binder and removing non-bonded new colourants (7, 12 b)from the surface such that a digital print (P) is formed with the first(12 a) and the new (12 b) colourants positioned side by side on thesurface (2).

24. The method as in any one of the preceding embodiments, wherein thecolourants (7) are applied by scattering.

25. The method as in any one of the preceding embodiments, wherein thecolourants (7) are arranged in a wood grain or a stone pattern.

26. The method as in any one of the preceding embodiments, wherein thesurface and the colourants are pressed and cured to a hard surface withan embossed (17) structure.

27. The method as in any one of the preceding embodiments, wherein thecolourants (7) are macro colourant particles (64) larger than 20microns.

28. The method as in any one of the preceding embodiments, wherein thecolourants (7) are pressed into the surface (2).

29 The method as in any one of the preceding embodiments, wherein thesurface (2) is a part of a panel (1) that is a laminate or wood floor, apowder based floor, a tile or a LVT floor.

30. An equipment (40) to provide a digital print (P) on a surface (2),comprising a digital drop application head (30′), a dry ink applicationstation (27), and a dry ink removal station (28) wherein:

-   -   the digital drop application head (30′) is adapted to apply        liquid blank ink (11) on the surface (2);    -   the dry ink application station (27) is adapted to apply dry ink        (15) comprising colourants (7) on the surface (2);    -   the blank ink (11) is adapted to bond a part of the dry ink (15)        to the surface (2); and    -   the dry ink removal station (28) is adapted to remove the        non-bonded colourants (7) from the surface (2).

31. An equipment as in embodiment 30, wherein the surface (2) is a partof a panel (1).

32. An equipment as in embodiments 30 or 31, wherein the dry ink (15)comprises a resin.

33. An equipment as in any one of the embodiments 30-32, wherein theblank ink (11) is water based.

34. An equipment as in any one of the embodiments 30-33, wherein theblank ink (11) is exposed to increased temperature after application.

35. Dry ink (15) comprising macro colourant particles (64) for bondingto a liquid print (P) applied on a surface (2) wherein the macrocolourant particles (64) comprise a particle body (66) and colourpigments (12) attached to the particle body (66).

36. Dry ink as in embodiment 35, wherein the macro colourant particles(64) are larger than 20 microns.

37. Dry ink as in embodiments 35 or 36, wherein the particle body (66)is a mineral particle (63), a fibre (61) or a thermosetting resin (13).

38. Dry ink as in embodiments 35 or 36, wherein the particle body (66)is a mineral particle (63).

39. Dry ink as in embodiments 35 or 36, wherein, the particle body (66)is a fibre (61)

40. Dry ink as in any one of embodiments 35-39, wherein the particlebody (66) is coated with a resin.

41. Dry ink as in embodiment 40, wherein the resin is a thermosettingresin (13).

42. Dry ink as in any one of embodiments 35-41, wherein the liquid printis water based and applied by a digital drop application head (30′).

43. A panel (1) with a surface (2) comprising a digitally formed print(P) of macro colourants (64) comprising a particle body (66) and colourpigments (12) attached to the surface of the particle body (66) whereinthe colourants (7) are arrange in patterns with pigments (12) on anupper and lower surface of the particle body (66).

44. A panel as in embodiment 43, wherein the particle body (66)comprises fibres (61).

45. A panel as in embodiment 43, wherein the particle body (66) is amineral particle (63).

46. A panel as in any one of the embodiments 43-45, wherein the macrocolourants (64) have a particle size exceeding 20 microns.

47. A panel as in any one of the preceding embodiments 43-46, whereinthe macro courants (64) form a solid print with overlapping decorativeparticles.

48. A panel as in any one of the preceding embodiments 43-47, whereinthe pane (1) is a laminate or wood floor, a powder based floor, a tileor a LVT floor.

49. A method of forming a digital embossing (17) on a surface (2) bybonding hard press particles (67) to a carrier (68) comprising the stepsof:

-   -   providing a liquid binder pattern (BP) on the carrier (68) by a        digital drop application head (30′) that applies a liquid        substance (11) on the carrier;    -   applying the hard press particles (67) on the carrier (68) and        the binder pattern (BP) such that the hard press particles are        bonded to the carrier (68) by the liquid binder pattern (BP);    -   removing the non-bonded hard press particles (67) from the        carrier (68);    -   pressing the carrier (68) with the bonded hard press particles        (67) to the surface (2); and    -   removing the carrier (68) with the hard press particles (67)        from the pressed surface (2).

50. The method as in embodiment 49, wherein the press particles (67) aremineral particles (63).

51. The method as in embodiments 49 or 50, wherein the carrier is apaper or a foil.

52. The method as in any one of the preceding embodiments 49-51, whereinthe liquid substance is water based.

53. The method as in any one of the preceding embodiments 49-52, whereinthe surface (2) is a powder or a paper or a foil.

54. The method as in any one of the preceding embodiments 49-53, whereinthe surface (2) is a part of a panel (1).

55. A panel (1) having a surface (2) with a wood grain decor comprisinga first surface portion (S1) that is formed by a continuous basic layercomprising wood fibres (61 a) having a first colour and a second surfaceportion (S2) that is formed by wood fibres (61 b) having a second colourwherein the wood fibres (61 b) having the second colour are applied onand bonded to the continuous basic layer, and wherein the second surfaceportion (S2) covers a part of the first surface portion (S1).

56. The panel as in embodiment 55, wherein the continuous basic layer isa powder comprising a thermosetting resin

57. The panel as in embodiments 55 or 56, wherein the continuous basiclayer is a paper.

58. The panel as in any one of the embodiments 55-57, wherein the secondsurface portion (S2) comprises smaller fibres than the first surfaceportion (S1)

59. An equipment to provide a digital print (P) on a surface (2) with atransfer printing method, wherein the equipment comprises a digital dropapplication head (30′), a dry ink application unit (27), a dry inkremoval station (28) and a transfer surface (18) wherein:

-   -   the digital drop application head (30′) is adapted to apply        liquid blank ink (11) on the transfer surface (18);    -   the dry ink application unit (27) is adapted to apply dry ink        (15) comprising colourants on the transfer surface (18);    -   the blank ink (11) is adapted to bond a part of the dry ink (15)        to the transfer surface (18);    -   the dry ink removal station (28) is adapted to remove the        non-bonded dry ink from the transfer surface (18); and    -   the transfer surface (18) with the bonded dry ink is adapted to        be pressed against the surface (2).

60. An equipment as in embodiment 59, wherein the dry ink (15) comprisesa resin.

61. An equipment as in embodiments 59 or 60, wherein the blank ink (11)is water based.

62. An equipment as in any one of the embodiments 59-61, wherein theblank ink is exposed to increased temperature after application.

63. A press matrix (78) for forming an embossed structure (17) on apanel (1) wherein the press matrix comprises hard press particles (67)arranged in a pattern and bonded to a carrier (68) being a coated paperor a foil.

64. A press matrix (78) as in embodiment 63, wherein the hard pressparticles (67) are arranged on one side of the carrier and a print (P)is arranged on the opposite side of the carrier.

65. A press matrix (78) as in embodiments 63 or 64, wherein the hardpress participles (67) and the print (P) are coordinated such that an inregister embossed printed surface may be obtained when the press matrixis pressed against a panel surface (2).

66. A method of forming a digital print (P) on a surface (2) wherein themethod comprises the steps of applying powder of dry ink (15) comprisingcolourants (7) on the surface, bonding a part of the dry ink (15) powderto the surface (2) by a digital heating print head (80) such that thedigital print (P) is formed by the bonded dry ink colourants (7) andremoving non bonded dry ink (15) from the surface (2).

67. The method as in embodiment 66, wherein the dry ink (15) comprises aheat sensitive resin.

68. The method as in embodiments 66 or 67, wherein the surface (2)comprises a heat sensitive resin.

69. The method as in embodiments 67 or 68, wherein the heat sensitiveresin is a thermosetting or thermoplastic resin.

70. The method as in embodiment 69, wherein the heat sensitive resin isa thermosetting resin comprising melamine.

71. The method as in any one of the embodiments 66-69, wherein theheating print head (80) applies heat on a heat transfer foil (81).

72. The method as in embodiment 70, wherein the heat transfer foil (81)comprises copper or aluminium.

72. The method as in any one of the embodiments 66-68, wherein thesurface (2) is a part of a building panel preferably a part of a floorpanel (1).

73. The method as in any one of the embodiments 66-72, wherein the dryink (15) comprises mineral particles.

74. The method as in embodiment 73, wherein the dry ink (15) comprisesaluminium oxide particles.

75. A method of forming a digital print (P) on a surface (2) comprisingapplying drops (57) of blank ink (11) by a digital drop application head(30′) on the surface (2) and attaching colourants (7) to the drops (57)of the blank ink for forming the digital print (P) wherein the digitalprint (P) comprises another colour than the blank ink (11).

76. The method as in embodiment 75, wherein the other colour is formedby colourants (7) bonded to the surface (2) by the blank ink (11).

77. The method as in embodiments 75 or 76, wherein the blank ink (11) isessentially a transparent liquid substance comprising water.

78. The method as in any one of the embodiments 75-77, wherein the blankink (11) forms a first and a second part of the print (P) and whereinthe blank ink, the first and the second parts all comprise differentcolours.

79. The method as in any one of the embodiments 75-78, wherein thedigital print (P) comprises colourants (7) with different colourspositioned horizontally offset in the same plane.

80. The method as in any one of the embodiments 75-79, wherein thevertical extension (V2) of the colourants (7) exceeds the verticalextension (V1) of blank ink drops (57).

81. The method as in any one of the embodiments 75-80, wherein thedigitally applied blank ink drops (57) penetrate downwards and upwardsfrom the surface (2) after application.

82. The method as in any one of the embodiments 75-81, wherein the dropsof the blank ink (11) that provide a blank ink spot (57) on the surface(2) bonds colourants (7) having a size that is larger than the size ofblank ink spot (57).

83. The method as in any one of the embodiments 75-82, wherein the blankink (11) is applied in a raster pattern (R1-R4) and wherein the dry ink(15) is applied at random with overlapping colourants (7).

84. The method as in any one of the embodiments 75-83, wherein thehorizontal extension (H2) of individual colourants (7) exceeds thehorizontal extension (H1) of the ink spots (57) and the verticalextension (V2) of the dry ink layer, after the removal of the non-bondedparticles, exceeds preferably the vertical extension (V1) of blank inkspots (57).

While illustrative embodiments of the invention have been describedherein, the present invention is not limited to the various preferredembodiments described herein but includes any and all embodiments havingequivalent elements, modifications, omissions, combinations (e.g. ofaspects across various embodiments), adaptations and/or alterations aswould be appreciated by those in the art based on the presentdisclosure. The limitations in the claims are to be interpreted broadlybased on the language employed in the claims and not limited to theexamples described in the present specification or during prosecution ofthe application, which examples are to be construed as non-exclusive.

1-12. (canceled)
 13. A method of forming a digital print on a surface,wherein the method comprises: applying a powder of dry ink comprisingcolorants on the surface; bonding a part of the powder of dry ink to thesurface by heating a portion of a transfer surface such that the dry inkheats up and the digital print is formed by bonded colorants of the dryink; and removing non-bonded dry ink from the surface.
 14. The method asclaimed in claim 13, wherein said portion of the transfer surface isheated by a digital heating print head.
 15. The method as claimed inclaim 14, wherein the digital heating print head comprises a pluralityof heating elements.
 16. The method as claimed in claim 15, wherein theheating elements apply varying amounts of heat.
 17. The method asclaimed in claim 14, wherein the transfer surface is in contact with thedigital heating print head and the dry ink particles.
 18. The method asclaimed in claim 13, wherein the transfer surface is a heat transferfoil.
 19. The method as claimed in claim 18, wherein the heat transferfoil is a paper, a foil, or a textile material.
 20. The method asclaimed in claim 18, wherein the heat transfer foil comprises copper oraluminum.
 21. The method as claimed in claim 13, wherein the transfersurface comprises individual elements that are embedded in a heatinsulating carrier.
 22. The method as claimed in claim 13, wherein heatis provided to the dry ink through the transfer surface.
 23. The methodas claimed in claim 13, wherein said portion of the transfer surface isheated prior to the application of the dry ink to the surface.
 24. Themethod as claimed in claim 14, wherein the transfer surface is providedbetween the dry ink and the heating print head.
 25. The method asclaimed in claim 14, wherein the transfer surface slides against thedigital heating print head.
 26. The method as claimed in claim 13,wherein the surface is a board material, a powder, a paper, a foil, atextile material, a base coating, a metal, solid wood, wood veneer, awood based sheet material, cork, linoleum, polymer material, ceramic, acarpet or wall paper.
 27. The method as claimed in claim 13, wherein thesurface is said transfer surface.
 28. The method as claimed in claim 27,wherein the print is transferred from the transfer surface to areceiving surface.
 29. The method as claimed in claim 28, wherein theprint is pressed on the receiving surface by rollers.
 30. The method asclaimed in claim 28, wherein the receiving surface is a board material,a powder, a paper, a foil, a textile material, a base coating, a metal,solid wood, wood veneer, a wood based sheet material, cork, linoleum,polymer material, ceramic, a carpet or wall paper.
 31. The method asclaimed in claim 13, wherein at least one of a pre-pressing unit, vacuumapplied on the surface or oscillation is used for increasing a contactbetween the dry ink particles and the surface during the heat bonding.32. The method as claimed in claim 13, the method further comprising:applying a second powder of dry ink comprising colorants on a portionthe surface where the powder of dry ink was previously applied; bondinga part of the second powder of dry ink to the surface by heating aportion of a transfer surface such that the dry ink heats up and thedigital print is formed by bonded colorants of the dry ink; and removingnon-bonded dry ink from the surface.
 33. The method as claimed in claim13, wherein the dry resin or the surface comprises a heat sensitiveresin.